add missing inherited equation

src/main/jastadd/backend/API.jadd

@@ -93,6 +93,7 @@ aspect BackendAPI {
   inh boolean RelationComponent.isNavigable();
   eq Relation.getLeft().isNavigable() = getDirection().isNavigableLeftToRight();
   eq Relation.getRight().isNavigable() = getDirection().isNavigableRightToLeft();
+  eq Program.getChild().isNavigable() = false;
 
   syn boolean Direction.isNavigableRightToLeft() = true;
   eq RightDirection.isNavigableRightToLeft() = false;