Fix matching single constraint on reactivation after a logical has been assigned.

reactor/Core/src/jetbrains/mps/logic/reactor/core/RuleMatcher.kt

@@ -82,10 +82,18 @@ class RuleMatcher(val rule: Rule) {
                             }
                         }
 
-                        else                -> newNodes.add(fn)
+                        else                -> {
+                            newNodes.add(fn)
+                        }
                     }
                 }
 
+                if (newNodes.size == 1) {
+                    // only the root
+                    val rfn = newNodes.get(0)
+                    newNodes.addAll(rfn.expand(occ, genId + 1, rfn.matchingVacant(mask)))
+                }
+
                 return MatchFringe(newNodes, seen, genId + 1)
 
             } else {

reactor/Test/test/TestRuleMatcher.kt

@@ -86,6 +86,34 @@ class TestRuleMatcher {
         }
     }
 
+    @Test
+    fun testSameOccurrenceLogical() {
+        with(programWithRules(
+            rule("rule1",
+                headReplaced(
+                    constraint("foo", term("bar"))
+                ),
+                body(
+                    constraint("qux")
+                ))))
+        {
+            val X = metaLogical<Term>("X")
+            val x = X.logical()
+            val foo = occurrence("foo", x)
+            with(ruleMatcher().probe()) {
+
+                expand(foo)                                             }.apply {
+                matches().size shouldBe 0                               }.run {
+
+                x.set(term("bar"))
+
+                expand(foo)                                        }.apply {
+                matches().size shouldBe 1                               }.run {
+
+            }
+        }
+    }
+
     @Test
     fun testTermArgument() {
         with(programWithRules(