anchor.diff:  
     test_propagation_downstream_through_substitution_inner() {
       // always -> 1
  -    // LUB(1, 2) -> 3
  +    // subst(1, 2) -> 3
       var n1 = newNode(1);
       var n2 = newNode(2);
       var n3 = newNode(3);
  
positive.code:   }
  
    test_propagation_downstream_through_substitution_neither() {
      // LUB(1, 2) -> 3
      var n1 = newNode(1);
      var n2 = newNode(2);
      var n3 = newNode(3);
  
negative.code: 
    test_propagation_downstream_through_substitution_outer() {
      // always -> 2
      // subst(1, 2) -> 3
      var n1 = newNode(1);
      var n2 = newNode(2);
      var n3 = newNode(3);
  