B :- x:A coincide y:A where x.v = y.v & x.v < 3 map { v -> x.v + 1 }
C :- x:B coincide y:B where x.v = y.v map { v -> x.v }
A :- x:C coincide y:C where x.v = y.v map { v -> x.v }
D :- E unless after A where E.v = A.v