diff --git a/CMakeLists.txt b/CMakeLists.txt
index aeef1885..5c358c65 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -91,7 +91,8 @@ add_subdirectory(xo-unit)
 add_subdirectory(xo-pyunit)
 add_subdirectory(xo-callback)
 add_subdirectory(xo-alloc)
-add_subdirectory(xo-alloc2)  # experiment w/ sep iface,data
+add_subdirectory(xo-alloc2)   # experiment w/ sep iface,data
+add_subdirectory(xo-gc)
 add_subdirectory(xo-object)
 add_subdirectory(xo-object2)  # experiment w/ facet object model
 add_subdirectory(xo-ordinaltree)
diff --git a/xo-alloc2/include/xo/alloc2/alloc/AllocError.hpp b/xo-alloc2/include/xo/alloc2/AllocError.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/alloc/AllocError.hpp
rename to xo-alloc2/include/xo/alloc2/AllocError.hpp
diff --git a/xo-alloc2/include/xo/alloc2/alloc/AllocHeader.hpp b/xo-alloc2/include/xo/alloc2/AllocHeader.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/alloc/AllocHeader.hpp
rename to xo-alloc2/include/xo/alloc2/AllocHeader.hpp
diff --git a/xo-alloc2/include/xo/alloc2/alloc/AllocHeaderConfig.hpp b/xo-alloc2/include/xo/alloc2/AllocHeaderConfig.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/alloc/AllocHeaderConfig.hpp
rename to xo-alloc2/include/xo/alloc2/AllocHeaderConfig.hpp
diff --git a/xo-alloc2/include/xo/alloc2/alloc/AllocInfo.hpp b/xo-alloc2/include/xo/alloc2/AllocInfo.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/alloc/AllocInfo.hpp
rename to xo-alloc2/include/xo/alloc2/AllocInfo.hpp
diff --git a/xo-alloc2/include/xo/alloc2/alloc/AllocRange.hpp b/xo-alloc2/include/xo/alloc2/AllocRange.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/alloc/AllocRange.hpp
rename to xo-alloc2/include/xo/alloc2/AllocRange.hpp
diff --git a/xo-alloc2/include/xo/alloc2/Collector.hpp b/xo-alloc2/include/xo/alloc2/Collector.hpp
deleted file mode 100644
index 45c7fdb5..00000000
--- a/xo-alloc2/include/xo/alloc2/Collector.hpp
+++ /dev/null
@@ -1,13 +0,0 @@
-/** @file Collector.hpp
- *
- *  @author Roland Conybeare, Dec 2025
- **/
-
-#pragma once
-
-#include "gc/ACollector.hpp"
-#include "gc/ICollector_Any.hpp"
-#include "gc/ICollector_Xfer.hpp"
-#include "gc/RCollector.hpp"
-
-/* end Collector.hpp */
diff --git a/xo-alloc2/include/xo/alloc2/alloc/AAllocIterator.hpp b/xo-alloc2/include/xo/alloc2/alloc/AAllocIterator.hpp
index f2d332b3..29be0a30 100644
--- a/xo-alloc2/include/xo/alloc2/alloc/AAllocIterator.hpp
+++ b/xo-alloc2/include/xo/alloc2/alloc/AAllocIterator.hpp
@@ -5,7 +5,7 @@
 
 #pragma once
 
-#include "alloc/AllocInfo.hpp"
+#include "AllocInfo.hpp"
 #include "cmpresult.hpp"
 #include <xo/facet/obj.hpp>
 
diff --git a/xo-alloc2/include/xo/alloc2/alloc/README b/xo-alloc2/include/xo/alloc2/alloc/README
deleted file mode 100644
index 6efbf852..00000000
--- a/xo-alloc2/include/xo/alloc2/alloc/README
+++ /dev/null
@@ -1,4 +0,0 @@
-AAllocator |<-- IAllocator_Any (D=DVariantPlaceholder)
-           |<-- IAllocator_Xfer<D,..>
-
-OObject<AAllocator,D> |<-- RAllocator<O>
diff --git a/xo-alloc2/include/xo/alloc2/arena/ArenaConfig.hpp b/xo-alloc2/include/xo/alloc2/arena/ArenaConfig.hpp
index 93fc35b8..7c2b6f80 100644
--- a/xo-alloc2/include/xo/alloc2/arena/ArenaConfig.hpp
+++ b/xo-alloc2/include/xo/alloc2/arena/ArenaConfig.hpp
@@ -5,7 +5,7 @@
 
 #pragma once
 
-#include "alloc/AllocHeaderConfig.hpp"
+#include "AllocHeaderConfig.hpp"
 //#include "alloc/AllocError.hpp"
 #include <string>
 #include <cstdint>
diff --git a/xo-alloc2/include/xo/alloc2/arena/DArena.hpp b/xo-alloc2/include/xo/alloc2/arena/DArena.hpp
index e44b6512..7c7196e1 100644
--- a/xo-alloc2/include/xo/alloc2/arena/DArena.hpp
+++ b/xo-alloc2/include/xo/alloc2/arena/DArena.hpp
@@ -6,8 +6,8 @@
 #pragma once
 
 #include "ArenaConfig.hpp"
-#include "alloc/AllocError.hpp"
-#include "alloc/AllocInfo.hpp"
+#include "AllocError.hpp"
+#include "AllocInfo.hpp"
 
 namespace xo {
     namespace mm {
diff --git a/xo-alloc2/include/xo/alloc2/arena/DArenaIterator.hpp b/xo-alloc2/include/xo/alloc2/arena/DArenaIterator.hpp
index 05cf7b7e..e25fbb8d 100644
--- a/xo-alloc2/include/xo/alloc2/arena/DArenaIterator.hpp
+++ b/xo-alloc2/include/xo/alloc2/arena/DArenaIterator.hpp
@@ -5,8 +5,8 @@
 
 #pragma once
 
-#include "alloc/AllocInfo.hpp"
-#include "alloc/AllocHeader.hpp"
+#include "AllocInfo.hpp"
+#include "AllocHeader.hpp"
 #include "cmpresult.hpp"
 
 namespace xo {
diff --git a/xo-alloc2/include/xo/alloc2/cmpresult.hpp b/xo-alloc2/include/xo/alloc2/cmpresult.hpp
index 0cc445c7..477e1dc0 100644
--- a/xo-alloc2/include/xo/alloc2/cmpresult.hpp
+++ b/xo-alloc2/include/xo/alloc2/cmpresult.hpp
@@ -11,9 +11,9 @@
 namespace xo {
     namespace mm {
         enum class comparison : int32_t {
-            invalid = -1,
-            comparable = 0,
-            incomparable = 1,
+            invalid      = -1,
+            comparable   =  0,
+            incomparable = +1,
         };
 
         extern const char * comparison2str(comparison x);
@@ -55,7 +55,7 @@ namespace xo {
 
             /* -1 -> invalid (sentinel)
              *  0 -> comparable
-             *  1 -> incomparable (e.g. iterators from different arenas)
+             * +1 -> incomparable (e.g. iterators from different arenas)
              */
             comparison   err_ = comparison::invalid;
             /* <0 -> lesser; 0 -> equal, >0 -> greater */
diff --git a/xo-alloc2/src/alloc2/AllocInfo.cpp b/xo-alloc2/src/alloc2/AllocInfo.cpp
index 76e899d7..9c4c8e7c 100644
--- a/xo-alloc2/src/alloc2/AllocInfo.cpp
+++ b/xo-alloc2/src/alloc2/AllocInfo.cpp
@@ -3,7 +3,7 @@
  *  @author Roland Conybeare, Dec 2025
  **/
 
-#include "alloc/AllocInfo.hpp"
+#include "AllocInfo.hpp"
 
 namespace xo {
     namespace mm {
diff --git a/xo-alloc2/src/alloc2/CMakeLists.txt b/xo-alloc2/src/alloc2/CMakeLists.txt
index 87327137..aabffe84 100644
--- a/xo-alloc2/src/alloc2/CMakeLists.txt
+++ b/xo-alloc2/src/alloc2/CMakeLists.txt
@@ -15,15 +15,6 @@ set(SELF_SRCS
     DArenaIterator.cpp
     IAllocIterator_DArenaIterator.cpp
 
-    ICollector_Any.cpp
-    IGCObject_Any.cpp
-    IAllocator_DX1Collector.cpp
-    ICollector_DX1Collector.cpp
-    IAllocIterator_DX1CollectorIterator.cpp
-
-    DX1Collector.cpp
-    DX1CollectorIterator.cpp
-
     )
 
 xo_add_shared_library4(${SELF_LIB} ${PROJECT_NAME}Targets ${PROJECT_VERSION} 1 ${SELF_SRCS})
diff --git a/xo-alloc2/utest/CMakeLists.txt b/xo-alloc2/utest/CMakeLists.txt
index ac5aa847..eacd19fd 100644
--- a/xo-alloc2/utest/CMakeLists.txt
+++ b/xo-alloc2/utest/CMakeLists.txt
@@ -7,15 +7,15 @@ set(UTEST_SRCS
     objectmodel.test.cpp
     arena.test.cpp
     DArenaIterator.test.cpp
-    Collector.test.cpp
-    DX1CollectorIterator.test.cpp
+#    Collector.test.cpp
+#    DX1CollectorIterator.test.cpp
     random_allocs.cpp
 )
 
 if (ENABLE_TESTING)
     xo_add_utest_executable(${UTEST_EXE} ${UTEST_SRCS})
-    xo_headeronly_dependency(${UTEST_EXE} randomgen)
     xo_self_dependency(${UTEST_EXE} xo_alloc2)
+    xo_headeronly_dependency(${UTEST_EXE} randomgen)
     xo_headeronly_dependency(${UTEST_EXE} indentlog)
     xo_headeronly_dependency(${UTEST_EXE} xo_facet)
     xo_external_target_dependency(${UTEST_EXE} Catch2 Catch2::Catch2)
diff --git a/xo-gc/CMakeLists.txt b/xo-gc/CMakeLists.txt
new file mode 100644
index 00000000..4480a1ad
--- /dev/null
+++ b/xo-gc/CMakeLists.txt
@@ -0,0 +1,32 @@
+# xo-gc/CMakeLists.txt
+
+cmake_minimum_required(VERSION 3.10)
+
+project(xo_gc VERSION 0.1)
+
+include(GNUInstallDirs)
+include(cmake/xo-bootstrap-macros.cmake)
+
+xo_cxx_toplevel_options3()
+
+# ----------------------------------------------------------------
+# c++ settings
+
+set(PROJECT_CXX_FLAGS "")
+#set(PROJECT_CXX_FLAGS "-fconcepts-diagnostics-depth=2")  # gcc-only!
+add_definitions(${PROJECT_CXX_FLAGS})
+
+# ----------------------------------------------------------------
+
+# must complete definition of expression lib before configuring examples
+add_subdirectory(src/gc)
+add_subdirectory(utest)
+#xo_export_cmake_config(${PROJECT_NAME} ${PROJECT_VERSION} ${PROJECT_NAME}Targets)
+
+# ----------------------------------------------------------------
+# docs targets depend on other library/utest/exec targets above,
+# --> must come after them.
+#
+#add_subdirectory(docs)
+
+# end CMakeLists.txt
diff --git a/xo-gc/cmake/xo-bootstrap-macros.cmake b/xo-gc/cmake/xo-bootstrap-macros.cmake
new file mode 100644
index 00000000..aba31169
--- /dev/null
+++ b/xo-gc/cmake/xo-bootstrap-macros.cmake
@@ -0,0 +1,35 @@
+# ----------------------------------------------------------------
+# for example:
+#   $ PREFIX=/usr/local   # for example
+#   $ cmake -DCMAKE_MODULE_PATH=prefix -DCMAKE_INSTALL_PREFIX=$PREFIX -B .build
+#
+# will get
+#   CMAKE_MODULE_PATH
+# from xo-cmake-config --cmake-module-path
+#
+# and expect .cmake macros in
+#   CMAKE_MODULE_PATH/xo_macros/xo_cxx.cmake
+# ----------------------------------------------------------------
+
+find_program(XO_CMAKE_CONFIG_EXECUTABLE NAMES xo-cmake-config REQUIRED)
+
+if ("${XO_CMAKE_CONFIG_EXECUTABLE}" STREQUAL "XO_CMAKE_CONFIG_EXECUTABLE-NOT_FOUND")
+    message(FATAL "could not find xo-cmake-config executable")
+endif()
+
+message(STATUS "XO_CMAKE_CONFIG_EXECUTABLE=${XO_CMAKE_CONFIG_EXECUTABLE}")
+
+if (NOT XO_SUBMODULE_BUILD)
+    if (("${CMAKE_MODULE_PATH}" STREQUAL "") OR ("${CMAKE_MODULE_PATH}" STREQUAL prefix))
+        # default to typical install location for xo-project-macros
+        execute_process(COMMAND ${XO_CMAKE_CONFIG_EXECUTABLE} --cmake-module-path OUTPUT_VARIABLE CMAKE_MODULE_PATH)
+        message(STATUS "CMAKE_MODULE_PATH=${CMAKE_MODULE_PATH}")
+    endif()
+endif()
+
+# needs to have been installed somewhere on CMAKE_MODULE_PATH,
+# (e.g. from xo-cmake with the same value for CMAKE_INSTALL_PREFIX)
+#
+include(xo_macros/xo_cxx)
+
+xo_cxx_bootstrap_message()
diff --git a/xo-gc/cmake/xo-gcConfig.cmake.in b/xo-gc/cmake/xo-gcConfig.cmake.in
new file mode 100644
index 00000000..c32a8368
--- /dev/null
+++ b/xo-gc/cmake/xo-gcConfig.cmake.in
@@ -0,0 +1,7 @@
+@PACKAGE_INIT@
+
+include(CMakeFindDependencyMacro)
+#find_dependency(indentlog)
+find_dependency(xo_alloc2)
+include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Targets.cmake")
+check_required_components("@PROJECT_NAME@")
diff --git a/xo-gc/include/xo/gc/Collector.hpp b/xo-gc/include/xo/gc/Collector.hpp
new file mode 100644
index 00000000..b4214036
--- /dev/null
+++ b/xo-gc/include/xo/gc/Collector.hpp
@@ -0,0 +1,13 @@
+/** @file Collector.hpp
+ *
+ *  @author Roland Conybeare, Dec 2025
+ **/
+
+#pragma once
+
+#include "detail/ACollector.hpp"
+#include "detail/ICollector_Any.hpp"
+#include "detail/ICollector_Xfer.hpp"
+#include "detail/RCollector.hpp"
+
+/* end Collector.hpp */
diff --git a/xo-alloc2/include/xo/alloc2/gc/DX1Collector.hpp b/xo-gc/include/xo/gc/DX1Collector.hpp
similarity index 99%
rename from xo-alloc2/include/xo/alloc2/gc/DX1Collector.hpp
rename to xo-gc/include/xo/gc/DX1Collector.hpp
index 5d2f614e..778f0518 100644
--- a/xo-alloc2/include/xo/alloc2/gc/DX1Collector.hpp
+++ b/xo-gc/include/xo/gc/DX1Collector.hpp
@@ -7,9 +7,9 @@
 
 #include "arena/ArenaConfig.hpp"
 #include "arena/DArena.hpp"
-#include "gc/generation.hpp"
-#include "gc/object_age.hpp"
-#include "gc/role.hpp"
+#include "generation.hpp"
+#include "object_age.hpp"
+#include "role.hpp"
 #include <memory>
 #include <array>
 
diff --git a/xo-alloc2/include/xo/alloc2/gc/DX1CollectorIterator.hpp b/xo-gc/include/xo/gc/DX1CollectorIterator.hpp
similarity index 98%
rename from xo-alloc2/include/xo/alloc2/gc/DX1CollectorIterator.hpp
rename to xo-gc/include/xo/gc/DX1CollectorIterator.hpp
index b510d30c..af1e867a 100644
--- a/xo-alloc2/include/xo/alloc2/gc/DX1CollectorIterator.hpp
+++ b/xo-gc/include/xo/gc/DX1CollectorIterator.hpp
@@ -5,8 +5,8 @@
 
 #pragma once
 
-#include "alloc/AllocInfo.hpp"
-#include "gc/generation.hpp"
+#include "AllocInfo.hpp"
+#include "generation.hpp"
 #include "arena/DArenaIterator.hpp"
 #include "cmpresult.hpp"
 
diff --git a/xo-alloc2/include/xo/alloc2/GCObject.hpp b/xo-gc/include/xo/gc/GCObject.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/GCObject.hpp
rename to xo-gc/include/xo/gc/GCObject.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gc/ACollector.hpp b/xo-gc/include/xo/gc/detail/ACollector.hpp
similarity index 97%
rename from xo-alloc2/include/xo/alloc2/gc/ACollector.hpp
rename to xo-gc/include/xo/gc/detail/ACollector.hpp
index da694e95..9c32125d 100644
--- a/xo-alloc2/include/xo/alloc2/gc/ACollector.hpp
+++ b/xo-gc/include/xo/gc/detail/ACollector.hpp
@@ -11,8 +11,8 @@
 #include <xo/facet/typeseq.hpp>
 #include <xo/facet/obj.hpp>
 
-#include "gc/generation.hpp"
-#include "gc/role.hpp"
+#include "generation.hpp"
+#include "role.hpp"
 
 #include <cstdint>
 #include <cstddef>
diff --git a/xo-alloc2/include/xo/alloc2/gc/IAllocIterator_DX1CollectorIterator.hpp b/xo-gc/include/xo/gc/detail/IAllocIterator_DX1CollectorIterator.hpp
similarity index 92%
rename from xo-alloc2/include/xo/alloc2/gc/IAllocIterator_DX1CollectorIterator.hpp
rename to xo-gc/include/xo/gc/detail/IAllocIterator_DX1CollectorIterator.hpp
index 686f9fcb..c221b580 100644
--- a/xo-alloc2/include/xo/alloc2/gc/IAllocIterator_DX1CollectorIterator.hpp
+++ b/xo-gc/include/xo/gc/detail/IAllocIterator_DX1CollectorIterator.hpp
@@ -5,8 +5,8 @@
 
 #pragma once
 
-#include "alloc/IAllocIterator_Xfer.hpp"
-#include "gc/DX1CollectorIterator.hpp"
+#include <xo/alloc2/alloc/IAllocIterator_Xfer.hpp>
+#include "xo/gc/DX1CollectorIterator.hpp"
 
 namespace xo {
     namespace mm { struct IAllocIterator_DX1CollectorIterator; }
diff --git a/xo-alloc2/include/xo/alloc2/gc/IAllocator_DX1Collector.hpp b/xo-gc/include/xo/gc/detail/IAllocator_DX1Collector.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gc/IAllocator_DX1Collector.hpp
rename to xo-gc/include/xo/gc/detail/IAllocator_DX1Collector.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gc/ICollector_Any.hpp b/xo-gc/include/xo/gc/detail/ICollector_Any.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gc/ICollector_Any.hpp
rename to xo-gc/include/xo/gc/detail/ICollector_Any.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gc/ICollector_DX1Collector.hpp b/xo-gc/include/xo/gc/detail/ICollector_DX1Collector.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gc/ICollector_DX1Collector.hpp
rename to xo-gc/include/xo/gc/detail/ICollector_DX1Collector.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gc/ICollector_Xfer.hpp b/xo-gc/include/xo/gc/detail/ICollector_Xfer.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gc/ICollector_Xfer.hpp
rename to xo-gc/include/xo/gc/detail/ICollector_Xfer.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gc/RCollector.hpp b/xo-gc/include/xo/gc/detail/RCollector.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gc/RCollector.hpp
rename to xo-gc/include/xo/gc/detail/RCollector.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gcobject/AGCObject.hpp b/xo-gc/include/xo/gc/gcobject/AGCObject.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gcobject/AGCObject.hpp
rename to xo-gc/include/xo/gc/gcobject/AGCObject.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gcobject/IGCObject_Any.hpp b/xo-gc/include/xo/gc/gcobject/IGCObject_Any.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gcobject/IGCObject_Any.hpp
rename to xo-gc/include/xo/gc/gcobject/IGCObject_Any.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gcobject/IGCObject_Xfer.hpp b/xo-gc/include/xo/gc/gcobject/IGCObject_Xfer.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gcobject/IGCObject_Xfer.hpp
rename to xo-gc/include/xo/gc/gcobject/IGCObject_Xfer.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gcobject/RGCObject.hpp b/xo-gc/include/xo/gc/gcobject/RGCObject.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gcobject/RGCObject.hpp
rename to xo-gc/include/xo/gc/gcobject/RGCObject.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gc/generation.hpp b/xo-gc/include/xo/gc/generation.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gc/generation.hpp
rename to xo-gc/include/xo/gc/generation.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gc/object_age.hpp b/xo-gc/include/xo/gc/object_age.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gc/object_age.hpp
rename to xo-gc/include/xo/gc/object_age.hpp
diff --git a/xo-alloc2/include/xo/alloc2/gc/role.hpp b/xo-gc/include/xo/gc/role.hpp
similarity index 100%
rename from xo-alloc2/include/xo/alloc2/gc/role.hpp
rename to xo-gc/include/xo/gc/role.hpp
diff --git a/xo-gc/src/gc/CMakeLists.txt b/xo-gc/src/gc/CMakeLists.txt
new file mode 100644
index 00000000..2d42c4c9
--- /dev/null
+++ b/xo-gc/src/gc/CMakeLists.txt
@@ -0,0 +1,21 @@
+# gc/CMakeLists.txt
+
+set(SELF_LIB xo_gc)
+set(SELF_SRCS
+
+    ICollector_Any.cpp
+    IGCObject_Any.cpp
+    IAllocator_DX1Collector.cpp
+    ICollector_DX1Collector.cpp
+    IAllocIterator_DX1CollectorIterator.cpp
+
+    DX1Collector.cpp
+    DX1CollectorIterator.cpp
+
+    )
+
+xo_add_shared_library4(${SELF_LIB} ${PROJECT_NAME}Targets ${PROJECT_VERSION} 1 ${SELF_SRCS})
+# note: deps here must also appear in cmake/xo_alloc2Config.cmake.in
+xo_dependency(${SELF_LIB} xo_alloc2)
+xo_dependency(${SELF_LIB} xo_facet)
+xo_dependency(${SELF_LIB} indentlog)
diff --git a/xo-alloc2/src/alloc2/DX1Collector.cpp b/xo-gc/src/gc/DX1Collector.cpp
similarity index 98%
rename from xo-alloc2/src/alloc2/DX1Collector.cpp
rename to xo-gc/src/gc/DX1Collector.cpp
index 141ce615..7e91ddbd 100644
--- a/xo-alloc2/src/alloc2/DX1Collector.cpp
+++ b/xo-gc/src/gc/DX1Collector.cpp
@@ -5,10 +5,10 @@
 
 #include "Allocator.hpp"
 #include "arena/IAllocator_DArena.hpp"
-#include "gc/DX1Collector.hpp"
-#include "gc/DX1CollectorIterator.hpp"
-#include "gc/generation.hpp"
-#include "gc/object_age.hpp"
+#include "xo/gc/DX1Collector.hpp"
+#include "xo/gc/DX1CollectorIterator.hpp"
+#include "generation.hpp"
+#include "object_age.hpp"
 #include <xo/facet/obj.hpp>
 #include <xo/indentlog/scope.hpp>
 #include <cassert>
diff --git a/xo-alloc2/src/alloc2/DX1CollectorIterator.cpp b/xo-gc/src/gc/DX1CollectorIterator.cpp
similarity index 98%
rename from xo-alloc2/src/alloc2/DX1CollectorIterator.cpp
rename to xo-gc/src/gc/DX1CollectorIterator.cpp
index 1c351b29..3942468b 100644
--- a/xo-alloc2/src/alloc2/DX1CollectorIterator.cpp
+++ b/xo-gc/src/gc/DX1CollectorIterator.cpp
@@ -3,8 +3,8 @@
  *  @author Roland Conybeare, Dec 2025
  **/
 
-#include "gc/DX1CollectorIterator.hpp"
-#include "gc/DX1Collector.hpp"
+#include "xo/gc/DX1CollectorIterator.hpp"
+#include "xo/gc/DX1Collector.hpp"
 #include <xo/indentlog/scope.hpp>
 #include <xo/indentlog/print/tag.hpp>
 
diff --git a/xo-alloc2/src/alloc2/IAllocIterator_DX1CollectorIterator.cpp b/xo-gc/src/gc/IAllocIterator_DX1CollectorIterator.cpp
similarity index 94%
rename from xo-alloc2/src/alloc2/IAllocIterator_DX1CollectorIterator.cpp
rename to xo-gc/src/gc/IAllocIterator_DX1CollectorIterator.cpp
index 85609f1e..9746870a 100644
--- a/xo-alloc2/src/alloc2/IAllocIterator_DX1CollectorIterator.cpp
+++ b/xo-gc/src/gc/IAllocIterator_DX1CollectorIterator.cpp
@@ -3,7 +3,7 @@
  *  @author Roland Conybeare, Dec 2025
  **/
 
-#include "gc/IAllocIterator_DX1CollectorIterator.hpp"
+#include "xo/gc/detail/IAllocIterator_DX1CollectorIterator.hpp"
 #include "AllocIterator.hpp"
 //#include <cassert>
 
diff --git a/xo-alloc2/src/alloc2/IAllocator_DX1Collector.cpp b/xo-gc/src/gc/IAllocator_DX1Collector.cpp
similarity index 94%
rename from xo-alloc2/src/alloc2/IAllocator_DX1Collector.cpp
rename to xo-gc/src/gc/IAllocator_DX1Collector.cpp
index 5ab1b003..d3e172fc 100644
--- a/xo-alloc2/src/alloc2/IAllocator_DX1Collector.cpp
+++ b/xo-gc/src/gc/IAllocator_DX1Collector.cpp
@@ -5,10 +5,10 @@
  *  See also ICollector_DX1Collector.cpp for collector facet
  **/
 
-#include "gc/IAllocator_DX1Collector.hpp"
-#include "gc/IAllocIterator_DX1CollectorIterator.hpp"
-#include "gc/DX1CollectorIterator.hpp"
-#include "arena/IAllocator_DArena.hpp"
+#include "detail/IAllocator_DX1Collector.hpp"
+#include "detail/IAllocIterator_DX1CollectorIterator.hpp"
+#include "DX1CollectorIterator.hpp"
+#include <xo/alloc2/arena/IAllocator_DArena.hpp>
 
 namespace xo {
     using xo::facet::with_facet;
diff --git a/xo-alloc2/src/alloc2/ICollector_Any.cpp b/xo-gc/src/gc/ICollector_Any.cpp
similarity index 96%
rename from xo-alloc2/src/alloc2/ICollector_Any.cpp
rename to xo-gc/src/gc/ICollector_Any.cpp
index 57700ad9..d3ea1fb8 100644
--- a/xo-alloc2/src/alloc2/ICollector_Any.cpp
+++ b/xo-gc/src/gc/ICollector_Any.cpp
@@ -3,7 +3,7 @@
  *  @author Roland Conybeare, Dec 2025
  **/
 
-#include "gc/ICollector_Any.hpp"
+#include "detail/ICollector_Any.hpp"
 #include <iostream>
 
 namespace xo {
diff --git a/xo-alloc2/src/alloc2/ICollector_DX1Collector.cpp b/xo-gc/src/gc/ICollector_DX1Collector.cpp
similarity index 99%
rename from xo-alloc2/src/alloc2/ICollector_DX1Collector.cpp
rename to xo-gc/src/gc/ICollector_DX1Collector.cpp
index 6be5696e..41e05f9d 100644
--- a/xo-alloc2/src/alloc2/ICollector_DX1Collector.cpp
+++ b/xo-gc/src/gc/ICollector_DX1Collector.cpp
@@ -5,7 +5,7 @@
  *  See also IAllocator_DX1Collector.cpp for allocator facet
  **/
 
-#include "gc/ICollector_DX1Collector.hpp"
+#include "xo/gc/detail/ICollector_DX1Collector.hpp"
 #include "GCObject.hpp"
 
 namespace xo {
diff --git a/xo-alloc2/src/alloc2/IGCObject_Any.cpp b/xo-gc/src/gc/IGCObject_Any.cpp
similarity index 100%
rename from xo-alloc2/src/alloc2/IGCObject_Any.cpp
rename to xo-gc/src/gc/IGCObject_Any.cpp
diff --git a/xo-gc/utest/CMakeLists.txt b/xo-gc/utest/CMakeLists.txt
new file mode 100644
index 00000000..c48dbdb5
--- /dev/null
+++ b/xo-gc/utest/CMakeLists.txt
@@ -0,0 +1,21 @@
+# xo-gc/utest/CMakeLists.txt
+#
+
+set(UTEST_EXE utest.gc)
+set(UTEST_SRCS
+    gc_utest_main.cpp
+    Collector.test.cpp
+    DX1CollectorIterator.test.cpp
+    random_allocs.cpp
+)
+
+if (ENABLE_TESTING)
+    xo_add_utest_executable(${UTEST_EXE} ${UTEST_SRCS})
+    xo_headeronly_dependency(${UTEST_EXE} randomgen)
+    xo_self_dependency(${UTEST_EXE} xo_gc)
+#    xo_headeronly_dependency(${UTEST_EXE} indentlog)
+    xo_headeronly_dependency(${UTEST_EXE} xo_facet)
+    xo_external_target_dependency(${UTEST_EXE} Catch2 Catch2::Catch2)
+endif()
+
+# end CMakeLists.txt
diff --git a/xo-alloc2/utest/Collector.test.cpp b/xo-gc/utest/Collector.test.cpp
similarity index 98%
rename from xo-alloc2/utest/Collector.test.cpp
rename to xo-gc/utest/Collector.test.cpp
index 119fac0f..f322c286 100644
--- a/xo-alloc2/utest/Collector.test.cpp
+++ b/xo-gc/utest/Collector.test.cpp
@@ -7,11 +7,11 @@
  *        see xo-object2/utest
  **/
 
-#include "Allocator.hpp"
+#include <xo/alloc2/Allocator.hpp>
 #include "Collector.hpp"
 #include "random_allocs.hpp"
-#include "gc/ICollector_DX1Collector.hpp"
-#include "gc/IAllocator_DX1Collector.hpp"
+#include "detail/ICollector_DX1Collector.hpp"
+#include "detail/IAllocator_DX1Collector.hpp"
 //#include "gc/DX1Collector.hpp"
 #include <xo/randomgen/xoshiro256.hpp>
 #include <xo/randomgen/random_seed.hpp>
diff --git a/xo-alloc2/utest/DX1CollectorIterator.test.cpp b/xo-gc/utest/DX1CollectorIterator.test.cpp
similarity index 97%
rename from xo-alloc2/utest/DX1CollectorIterator.test.cpp
rename to xo-gc/utest/DX1CollectorIterator.test.cpp
index 3ae405ee..ba3ba09c 100644
--- a/xo-alloc2/utest/DX1CollectorIterator.test.cpp
+++ b/xo-gc/utest/DX1CollectorIterator.test.cpp
@@ -3,11 +3,11 @@
  *  @author Roland Conybeare, Dec 2025
  **/
 
-#include "Allocator.hpp"
+#include <xo/alloc2/Allocator.hpp>
 #include "AllocIterator.hpp"
-#include "gc/DX1CollectorIterator.hpp"
-#include "gc/IAllocator_DX1Collector.hpp"
-#include "gc/IAllocIterator_DX1CollectorIterator.hpp"
+#include "DX1CollectorIterator.hpp"
+#include "detail/IAllocator_DX1Collector.hpp"
+#include "detail/IAllocIterator_DX1CollectorIterator.hpp"
 #include "arena/ArenaConfig.hpp"
 #include "padding.hpp"
 #include <xo/indentlog/scope.hpp>
@@ -17,7 +17,7 @@
 namespace xo {
     using xo::mm::AAllocator;
     using xo::mm::AAllocIterator;
-    using xo::mm::IAllocIterator_Any;
+//    using xo::mm::IAllocIterator_Any;
     using xo::mm::IAllocIterator_Xfer;
     using xo::mm::IAllocIterator_DX1CollectorIterator;
     using xo::mm::DX1Collector;
diff --git a/xo-gc/utest/gc_utest_main.cpp b/xo-gc/utest/gc_utest_main.cpp
new file mode 100644
index 00000000..8c426003
--- /dev/null
+++ b/xo-gc/utest/gc_utest_main.cpp
@@ -0,0 +1,6 @@
+/* file gc_utest_main.cpp */
+
+#define CATCH_CONFIG_MAIN
+#include "catch2/catch.hpp"
+
+/* end gc_utest_main.cpp */
diff --git a/xo-gc/utest/random_allocs.cpp b/xo-gc/utest/random_allocs.cpp
new file mode 100644
index 00000000..56d0cb85
--- /dev/null
+++ b/xo-gc/utest/random_allocs.cpp
@@ -0,0 +1,217 @@
+/** @file random_allocs.cpp
+ *
+ *  @author Roland Conybeare, Dec 2025
+ **/
+
+#include "random_allocs.hpp"
+#include "arena/DArena.hpp"
+#include "padding.hpp"
+#include <xo/indentlog/scope.hpp>
+#include <xo/indentlog/print/tag.hpp>
+#include <catch2/catch.hpp>
+#include <map>
+
+namespace utest {
+    using xo::mm::AllocInfo;
+    using xo::mm::DArena;
+    using xo::mm::ArenaConfig;
+    using xo::mm::padding;
+    using xo::rng::xoshiro256ss;
+    using xo::facet::obj;
+    using xo::scope;
+    using xo::xtag;
+    using std::uint32_t;
+    using std::byte;
+
+    /* remember an allocation result.
+     * application owns memory in [lo, lo+z)
+     */
+    struct Alloc {
+        Alloc() = default;
+        Alloc(byte * lo, size_t z) : lo_{lo}, z_{z} {}
+
+        byte * lo() const { return lo_; }
+        byte * hi() const { return lo_ + z_; }
+
+        byte * lo_ = nullptr;
+        size_t z_ = 0;
+    };
+
+    bool
+    AllocUtil::random_allocs(uint32_t n_alloc,
+                             bool catch_flag,
+                             xoshiro256ss * p_rgen,
+                             obj<AAllocator> mm)
+    {
+        scope log(XO_DEBUG(catch_flag), xtag("n-alloc", n_alloc));
+
+        /* track allocs. verify:
+         *  - allocs are non-overlapping
+         *  - allocs have valid alloc header
+         *  - allocs surrounded by guard bytes
+         *
+         * allocs sorted on Alloc::lo
+         */
+        std::map<const byte *, Alloc> allocs_by_lo_map;
+        /* allocs sorted on Alloc::hi */
+        std::map<const byte *, Alloc*> allocs_by_hi_map;
+
+        for (uint32_t i_alloc = 0; i_alloc < n_alloc; ++i_alloc) {
+            std::normal_distribution<double> ngen{5.0, 1.5};
+
+            double si = ngen(*p_rgen);
+            double zi = ::pow(2.0, si);
+            std::size_t z = ::ceil(zi);
+
+            bool ok_flag = true;
+
+            std::byte * mem = mm.alloc(z);
+
+            log && log(xtag("i_alloc", i_alloc),
+                       xtag("si", si),
+                       xtag("zi", zi),
+                       xtag("mem", mem));
+            log && log(xtag("used", mm.allocated()),
+                       xtag("avail", mm.available()),
+                       xtag("commit", mm.committed()),
+                       xtag("resv", mm.reserved()));
+
+
+            REQUIRE_ORFAIL(ok_flag, catch_flag, mem != nullptr);
+            REQUIRE_ORFAIL(ok_flag, catch_flag, mm.contains(mem));
+            REQUIRE_ORFAIL(ok_flag, catch_flag, mm.last_error().error_seq_ == 0);
+            REQUIRE_ORFAIL(ok_flag, catch_flag, mm.last_error().error_ == xo::mm::error::none);
+
+            {
+                auto ix = allocs_by_lo_map.lower_bound(mem);
+                if (ix != allocs_by_lo_map.end()) {
+                    REQUIRE_ORFAIL(ok_flag, catch_flag, (ix->first > mem + z));
+                }
+            }
+
+            {
+                auto ix = allocs_by_hi_map.upper_bound(mem);
+                if (ix != allocs_by_hi_map.end()) {
+                    --ix;
+                    REQUIRE_ORFAIL(ok_flag, catch_flag, (ix->first < mem));
+                }
+            }
+
+            allocs_by_lo_map[mem] = Alloc(mem, z);
+            allocs_by_hi_map[mem + z] = &(allocs_by_lo_map[mem]);
+
+            /* verify we can recover alloc info */
+            AllocInfo info = mm.alloc_info(mem);
+
+            REQUIRE_ORFAIL(ok_flag, catch_flag, info.is_valid());
+
+            REQUIRE_ORFAIL(ok_flag, catch_flag,
+                           info.size() == padding::with_padding(z));
+
+            /* age isn't configured -> 0 = sentinel */
+            REQUIRE_ORFAIL(ok_flag, catch_flag, info.age() == 0);
+            /* tseq isn't configured -> 0 = sentinel */
+            REQUIRE_ORFAIL(ok_flag, catch_flag, info.tseq() == 0);
+
+            if ((info.p_config_->guard_z_ > 0)
+                || info.guard_lo().first
+                || info.guard_lo().second
+                || info.guard_hi().first
+                || info.guard_hi().second)
+            {
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_lo().first != nullptr);
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_lo().second != nullptr);
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_lo().first + info.guard_z()
+                               == info.guard_lo().second);
+
+                for (const byte * p = info.guard_lo().first;
+                     p != info.guard_lo().second; ++p)
+                {
+                    REQUIRE_ORFAIL(ok_flag, catch_flag, (char)*p == info.guard_byte());
+                }
+
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_hi().first != nullptr);
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_hi().second != nullptr);
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_hi().first + info.guard_z()
+                               == info.guard_hi().second);
+
+                for (const byte * p = info.guard_hi().first;
+                     p != info.guard_hi().second; ++p)
+                {
+                    REQUIRE_ORFAIL(ok_flag, catch_flag, (char)*p == info.guard_byte());
+                }
+
+
+            } else {
+                /* control here only if all of:
+                 *  - guard_z is zero
+                 *  - guard_lo empty
+                 *  - guard_hi empty
+                 */
+
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_lo().first == nullptr);
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_lo().second == nullptr);
+
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_hi().first == nullptr);
+                REQUIRE_ORFAIL(ok_flag, catch_flag,
+                               info.guard_hi().second == nullptr);
+
+            }
+
+            /** scratch arena for iterators **/
+            DArena scratch_mm = DArena::map(ArenaConfig{.name_ = "scratch",
+                                                        .size_ = 4*1024,
+                                                        .hugepage_z_ = 4*1024 });
+            auto range = mm.alloc_range(scratch_mm);
+
+            /* limit iteration test to a few cases:
+             *  - 1st loop
+             *  - median loop
+             *  - last loop
+             */
+            if (i_alloc == 0 || i_alloc == n_alloc || 2*i_alloc == n_alloc)
+            {
+                /* verify iteration visits all the allocs, exactly once */
+
+                /* temp copy; remove allocs from this map as we encounter
+                 * them via range iteration below
+                 */
+                auto alloc_map = allocs_by_lo_map;
+
+                if (log) {
+                    log(xtag("allocs_by_lo_map.size", allocs_by_lo_map.size()));
+
+                    for (auto & kv : allocs_by_lo_map) {
+                        log(xtag("key", kv.first), xtag("value", kv.second.lo()), xtag("hi", kv.second.hi()));
+                    }
+                }
+
+                for (AllocInfo info : range) {
+                    INFO(tostr(xtag("alloc_map.size", alloc_map.size()),
+                               xtag("i_alloc", i_alloc)));
+                    INFO(tostr(xtag("payload.first", info.payload().first)));
+
+                    const std::byte * alloc_lo = info.payload().first;
+
+                    REQUIRE_ORFAIL(ok_flag, catch_flag,
+                                   alloc_map.find(alloc_lo) != alloc_map.end());
+
+                    alloc_map.erase(alloc_lo);
+                }
+            }
+        }
+
+        return true;
+    }
+}
+
+/* end random_allocs.cpp */
diff --git a/xo-gc/utest/random_allocs.hpp b/xo-gc/utest/random_allocs.hpp
new file mode 100644
index 00000000..ab0afc4e
--- /dev/null
+++ b/xo-gc/utest/random_allocs.hpp
@@ -0,0 +1,45 @@
+/** @file random_allocs.hpp
+ *
+ *  @author Roland Conybeare, Dec 2025
+ **/
+
+#pragma once
+
+#include "Allocator.hpp"
+#include <xo/facet/obj.hpp>
+#include <xo/randomgen/xoshiro256.hpp>
+
+namespace utest {
+
+/* note: trivial REQUIRE() call in else branch bc we still want
+ *       catch2 to count assertions when verification succeeds
+ */
+#  define REQUIRE_ORCAPTURE(ok_flag, catch_flag, expr) \
+    if (catch_flag) {                                  \
+        REQUIRE((expr));                               \
+    } else {                                           \
+        REQUIRE(true);                                 \
+        ok_flag &= (expr);                             \
+    }
+
+#  define REQUIRE_ORFAIL(ok_flag, catch_flag, expr)    \
+    REQUIRE_ORCAPTURE(ok_flag, catch_flag, expr);      \
+    if (!ok_flag)                                      \
+        return ok_flag
+
+
+
+    struct AllocUtil {
+        using AAllocator = xo::mm::AAllocator;
+
+        /** generate a random sequence of allocations.
+         *  verify allocator behavior
+         **/
+        static bool random_allocs(std::uint32_t n_alloc,
+                                  bool catch_flag,
+                                  xo::rng::xoshiro256ss * p_rgen,
+                                  xo::facet::obj<AAllocator> alloc);
+    };
+}
+
+/* end random_allocs.hpp */
diff --git a/xo-object2/include/xo/object2/DList.hpp b/xo-object2/include/xo/object2/DList.hpp
index a9d02955..9710defb 100644
--- a/xo-object2/include/xo/object2/DList.hpp
+++ b/xo-object2/include/xo/object2/DList.hpp
@@ -3,7 +3,7 @@
  *  @author Roland Conybeare, Dec 2025
  **/
 
-#include "xo/alloc2/GCObject.hpp"
+#include "xo/gc/GCObject.hpp"
 //#include "xo/alloc2/gcobject/RGCObject.hpp"
 #include "xo/facet/obj.hpp"
 
diff --git a/xo-object2/include/xo/object2/IGCObject_DFloat.hpp b/xo-object2/include/xo/object2/IGCObject_DFloat.hpp
index 6a96dcf5..b00873c8 100644
--- a/xo-object2/include/xo/object2/IGCObject_DFloat.hpp
+++ b/xo-object2/include/xo/object2/IGCObject_DFloat.hpp
@@ -6,8 +6,8 @@
 #pragma once
 
 #include <xo/alloc2/alloc/AAllocator.hpp>
-#include <xo/alloc2/gcobject/AGCObject.hpp>
-#include <xo/alloc2/gcobject/IGCObject_Xfer.hpp>
+#include <xo/gc/gcobject/AGCObject.hpp>
+#include <xo/gc/gcobject/IGCObject_Xfer.hpp>
 #include "DFloat.hpp"
 
 namespace xo {
diff --git a/xo-object2/include/xo/object2/IGCObject_DInteger.hpp b/xo-object2/include/xo/object2/IGCObject_DInteger.hpp
index 765d2d96..858856b9 100644
--- a/xo-object2/include/xo/object2/IGCObject_DInteger.hpp
+++ b/xo-object2/include/xo/object2/IGCObject_DInteger.hpp
@@ -6,8 +6,8 @@
 #pragma once
 
 #include "xo/alloc2/alloc/AAllocator.hpp"
-#include <xo/alloc2/gcobject/AGCObject.hpp>
-#include <xo/alloc2/gcobject/IGCObject_Xfer.hpp>
+#include <xo/gc/gcobject/AGCObject.hpp>
+#include <xo/gc/gcobject/IGCObject_Xfer.hpp>
 #include "DInteger.hpp"
 
 namespace xo {
diff --git a/xo-object2/include/xo/object2/IGCObject_DList.hpp b/xo-object2/include/xo/object2/IGCObject_DList.hpp
index dc3ffa63..b4f47c8e 100644
--- a/xo-object2/include/xo/object2/IGCObject_DList.hpp
+++ b/xo-object2/include/xo/object2/IGCObject_DList.hpp
@@ -7,12 +7,9 @@
 
 #include <xo/alloc2/alloc/AAllocator.hpp>
 #include <xo/alloc2/alloc/RAllocator.hpp>
-#include <xo/alloc2/Collector.hpp>
-//#include <xo/alloc2/gc/ACollector.hpp>
-//#include <xo/alloc2/gc/ICollector_Any.hpp>
-//#include <xo/alloc2/gc/RCollector.hpp>
-#include <xo/alloc2/gcobject/AGCObject.hpp>
-#include <xo/alloc2/gcobject/IGCObject_Xfer.hpp>
+#include <xo/gc/Collector.hpp>
+#include <xo/gc/gcobject/AGCObject.hpp>
+#include <xo/gc/gcobject/IGCObject_Xfer.hpp>
 #include "DList.hpp"
 
 namespace xo {
diff --git a/xo-object2/src/object2/CMakeLists.txt b/xo-object2/src/object2/CMakeLists.txt
index f3c1382a..644216aa 100644
--- a/xo-object2/src/object2/CMakeLists.txt
+++ b/xo-object2/src/object2/CMakeLists.txt
@@ -9,5 +9,5 @@ set(SELF_SRCS
 
 xo_add_shared_library4(${SELF_LIB} ${PROJECT_NAME}Targets ${PROJECT_VERSION} 1 ${SELF_SRCS})
 # note: deps here must also appear in cmake/xo_alloc2Config.cmake.in
-xo_dependency(${SELF_LIB} xo_alloc2)
+xo_dependency(${SELF_LIB} xo_gc)
 #xo_dependency(${SELF_LIB} indentlog)