# non-projective edge (a-layer)
a-node $n2 :=
[ !ancestor $ref0, ((order-precedes $ref0 and order-follows $ref1) or (order-follows $ref0 and order-precedes $ref1)) ];

a-node $ref0 :=
[ same-tree-as $n2,
      a-node $ref1 := [  ] ];
  >> give distinct $ref1
  >> give count()
