diff --git a/lang/unification/simplesolver.go b/lang/unification/simplesolver.go
index 511b2fe3..e6c20b7b 100644
--- a/lang/unification/simplesolver.go
+++ b/lang/unification/simplesolver.go
@@ -195,6 +195,16 @@ func SimpleInvariantSolver(invariants []interfaces.Invariant, expected []interfa
 		return unsolved, result
 	}
 
+	// build a static list that won't get consumed
+	fnInvariants := []*interfaces.EqualityWrapFuncInvariant{}
+	for _, x := range equalities {
+		eq, ok := x.(*interfaces.EqualityWrapFuncInvariant)
+		if !ok {
+			continue
+		}
+		fnInvariants = append(fnInvariants, eq)
+	}
+
 	logf("%s: starting loop with %d equalities", Name, len(equalities))
 	// run until we're solved, stop consuming equalities, or type clash
 Loop:
@@ -481,6 +491,78 @@ Loop:
 					}
 				}
 
+				// is there another EqualityWrapFuncInvariant with the same Expr1 pointer?
+				for _, fn := range fnInvariants {
+					if eq.Expr1 != fn.Expr1 {
+						continue
+					}
+					// wow they match
+
+					if len(eq.Expr2Ord) != len(fn.Expr2Ord) {
+						return nil, fmt.Errorf("func arg count differs")
+					}
+					for i := range eq.Expr2Ord {
+						lhsName := eq.Expr2Ord[i]
+						lhsExpr := eq.Expr2Map[lhsName] // assume key exists
+						rhsName := fn.Expr2Ord[i]
+						rhsExpr := fn.Expr2Map[rhsName] // assume key exists
+
+						lhsTyp, lhsExists := solved[lhsExpr]
+						rhsTyp, rhsExists := solved[rhsExpr]
+
+						// both solved or both unsolved we skip
+						if lhsExists && !rhsExists { // teach rhs
+							typ, exists := funcPartials[eq.Expr1][rhsExpr]
+							if !exists {
+								funcPartials[eq.Expr1][rhsExpr] = lhsTyp // learn!
+								continue
+							}
+							if err := typ.Cmp(lhsTyp); err != nil {
+								return nil, errwrap.Wrapf(err, "can't unify, invariant illogicality with partial func arg")
+							}
+						}
+						if rhsExists && !lhsExists { // teach lhs
+							typ, exists := funcPartials[eq.Expr1][lhsExpr]
+							if !exists {
+								funcPartials[eq.Expr1][lhsExpr] = rhsTyp // learn!
+								continue
+							}
+							if err := typ.Cmp(rhsTyp); err != nil {
+								return nil, errwrap.Wrapf(err, "can't unify, invariant illogicality with partial func arg")
+							}
+						}
+					}
+
+					lhsExpr := eq.Expr2Out
+					rhsExpr := fn.Expr2Out
+
+					lhsTyp, lhsExists := solved[lhsExpr]
+					rhsTyp, rhsExists := solved[rhsExpr]
+
+					// both solved or both unsolved we skip
+					if lhsExists && !rhsExists { // teach rhs
+						typ, exists := funcPartials[eq.Expr1][rhsExpr]
+						if !exists {
+							funcPartials[eq.Expr1][rhsExpr] = lhsTyp // learn!
+							continue
+						}
+						if err := typ.Cmp(lhsTyp); err != nil {
+							return nil, errwrap.Wrapf(err, "can't unify, invariant illogicality with partial func arg")
+						}
+					}
+					if rhsExists && !lhsExists { // teach lhs
+						typ, exists := funcPartials[eq.Expr1][lhsExpr]
+						if !exists {
+							funcPartials[eq.Expr1][lhsExpr] = rhsTyp // learn!
+							continue
+						}
+						if err := typ.Cmp(rhsTyp); err != nil {
+							return nil, errwrap.Wrapf(err, "can't unify, invariant illogicality with partial func arg")
+						}
+					}
+
+				}
+
 				// can we solve anything?
 				var ready = true // assume ready
 				typ := &types.Type{
diff --git a/lang/unification/simplesolver_test.go b/lang/unification/simplesolver_test.go
index cf46026f..8a2716f2 100644
--- a/lang/unification/simplesolver_test.go
+++ b/lang/unification/simplesolver_test.go
@@ -96,6 +96,70 @@ func TestSimpleSolver1(t *testing.T) {
 			//experr: ErrAmbiguous,
 		})
 	}
+	{
+		// ?1 = func(x ?2) ?3
+		// ?1 = func(arg0 str) ?4
+		// ?3 = str # needed since we don't know what the func body is
+		expr1 := &interfaces.ExprAny{} // ?1
+		expr2 := &interfaces.ExprAny{} // ?2
+		expr3 := &interfaces.ExprAny{} // ?3
+		expr4 := &interfaces.ExprAny{} // ?4
+
+		arg0 := &interfaces.ExprAny{} // arg0
+
+		invarA := &interfaces.EqualityWrapFuncInvariant{
+			Expr1: expr1, // Expr
+			Expr2Map: map[string]interfaces.Expr{ // map[string]Expr
+				"x": expr2,
+			},
+			Expr2Ord: []string{"x"}, // []string
+			Expr2Out: expr3,         // Expr
+		}
+
+		invarB := &interfaces.EqualityWrapFuncInvariant{
+			Expr1: expr1, // Expr
+			Expr2Map: map[string]interfaces.Expr{ // map[string]Expr
+				"arg0": arg0,
+			},
+			Expr2Ord: []string{"arg0"}, // []string
+			Expr2Out: expr4,            // Expr
+		}
+
+		invarC := &interfaces.EqualsInvariant{
+			Expr: expr3,
+			Type: types.NewType("str"),
+		}
+
+		invarD := &interfaces.EqualsInvariant{
+			Expr: arg0,
+			Type: types.NewType("str"),
+		}
+
+		testCases = append(testCases, test{
+			name: "dual functions",
+			invariants: []interfaces.Invariant{
+				invarA,
+				invarB,
+				invarC,
+				invarD,
+			},
+			expected: []interfaces.Expr{
+				expr1,
+				expr2,
+				expr3,
+				expr4,
+				arg0,
+			},
+			fail: false,
+			expect: map[interfaces.Expr]*types.Type{
+				expr1: types.NewType("func(str) str"),
+				expr2: types.NewType("str"),
+				expr3: types.NewType("str"),
+				expr4: types.NewType("str"),
+				arg0:  types.NewType("str"),
+			},
+		})
+	}
 
 	names := []string{}
 	for index, tc := range testCases { // run all the tests