if e1 = e2 then ac_stacks f ~si r c m1 m2 else f false
| B.GRef (B.Entry (e1, B.Abst _) :: _, _),
B.GRef (B.Entry (e2, B.Abst _) :: _, _) ->
if e1 = e2 then ac_stacks f ~si r c m1 m2 else f false
| B.GRef (B.Entry (e1, B.Abst _) :: _, _),
B.GRef (B.Entry (e2, B.Abst _) :: _, _) ->