diff --git a/xo-procedure2/include/xo/procedure2/init_primitives.hpp b/xo-procedure2/include/xo/procedure2/init_primitives.hpp
index d2d51a59..6747fa6b 100644
--- a/xo-procedure2/include/xo/procedure2/init_primitives.hpp
+++ b/xo-procedure2/include/xo/procedure2/init_primitives.hpp
@@ -15,13 +15,20 @@ namespace xo {
 #endif
 
         struct Primitives {
-            /** polymorphich multiply
+            /** polymorphic multiply
              *
              *  TODO: this will want to move to xo-numeric/
              *        so we can dispatch on vector, matrix, function types
              **/
             static DPrimitive_gco_2_gco_gco s_mul_gco_gco_pm;
 
+            /** polymorphic subtract
+             *
+             *  TODO: this will want to move to xo-numeric/
+             *        so we can dispatch on vector, matrix, function types
+             **/
+            static DPrimitive_gco_2_gco_gco s_sub_gco_gco_pm;
+
             /** polymorphic equality comparison
              *
              *  TODO: this will want to move to x-numeric/
diff --git a/xo-procedure2/src/procedure2/init_primitives.cpp b/xo-procedure2/src/procedure2/init_primitives.cpp
index c1eceada..f3759f4b 100644
--- a/xo-procedure2/src/procedure2/init_primitives.cpp
+++ b/xo-procedure2/src/procedure2/init_primitives.cpp
@@ -99,6 +99,66 @@ namespace xo {
             return obj<AGCObject>();
         }
 
+        obj<AGCObject>
+        sub_gco_gco(obj<ARuntimeContext> rcx,
+                    obj<AGCObject> x_gco,
+                    obj<AGCObject> y_gco)
+        {
+            using xo::reflect::typeseq;
+
+            obj<AAllocator> mm = rcx.allocator();
+
+            // PLACEHOLDER
+
+            // TODO:
+            // 1. move this to xo-numeric2/ when available
+            // 2. at that point will require polymorphic dispatch
+            //    on argument representations, analogous to dispatch
+            //    in FacetRegistry
+
+            typeseq x_tseq = x_gco._typeseq();
+            typeseq y_tseq = y_gco._typeseq();
+
+            // FOR NOW: just test runtime values
+            //
+            if (x_tseq == typeseq::id<DInteger>()) {
+                // i64 * ..
+                long   x = GCObjectConversion<long>::from_gco(mm, x_gco);
+
+                if (y_tseq == typeseq::id<DInteger>()) {
+                    // i64 * i64
+                    long   y = GCObjectConversion<long>::from_gco(mm, y_gco);
+
+                    return DInteger::box<AGCObject>(mm, x - y);
+                } else if (y_tseq == typeseq::id<DFloat>()) {
+                    // i64 * f64
+                    double y = GCObjectConversion<double>::from_gco(mm, y_gco);
+
+                    return DFloat::box<AGCObject>(mm, x - y);
+                }
+            } else if (x_tseq == typeseq::id<DFloat>()) {
+                if (y_tseq == typeseq::id<DInteger>()) {
+                    // f64 * i64.
+                    double x = GCObjectConversion<double>::from_gco(mm, x_gco);
+                    long   y = GCObjectConversion<long>::from_gco(mm, y_gco);
+
+                    return DFloat::box<AGCObject>(mm, x - y);
+                } else if (y_tseq == typeseq::id<DFloat>()) {
+                    // f64 * f64.
+                    double x = GCObjectConversion<double>::from_gco(mm, x_gco);
+                    double y = GCObjectConversion<double>::from_gco(mm, y_gco);
+
+                    return DFloat::box<AGCObject>(mm, x - y);
+                }
+            }
+
+            // here: error
+            throw std::runtime_error(tostr("sub_gco_gco: unexpected argument types xt,yt",
+                                           xtag("x.tseq", x_tseq),
+                                           xtag("y.tseq", y_tseq)));
+            return obj<AGCObject>();
+        }
+
         obj<AGCObject>
         equal_gco_gco(obj<ARuntimeContext> rcx,
                       obj<AGCObject> x_gco,
@@ -113,7 +173,7 @@ namespace xo {
             // TODO
             // 1. move this to xo-numeric2/ when available
             // 2. at that point will require polymorphic dispatch on argument representations.
-            // 
+            //
 
             typeseq x_tseq = x_gco._typeseq();
             typeseq y_tseq = y_gco._typeseq();
@@ -150,7 +210,7 @@ namespace xo {
                     return DFloat::box<AGCObject>(mm, x == y);
                 }
             }
-            
+
             // here: error
             throw std::runtime_error(tostr("mul_gco_gco: unexpected argument types xt,yt",
                                            xtag("x.tseq", x_tseq),
@@ -198,6 +258,9 @@ namespace xo {
         DPrimitive_gco_2_gco_gco
         Primitives::s_mul_gco_gco_pm("_mul", &mul_gco_gco);
 
+        DPrimitive_gco_2_gco_gco
+        Primitives::s_sub_gco_gco_pm("_sub", &sub_gco_gco);
+
         DPrimitive_gco_2_gco_gco
         Primitives::s_equal_gco_gco_pm("_equal", &equal_gco_gco);