let filter_comparison ival_filter e1 ~cond_expr =
match e1 with
| Top _ -> e1
| Map m1 ->
try
let k,v2 = find_lonely_key cond_expr in
let v1 = find_or_bottom k m1 in
Map (add_or_bottom k (ival_filter v1 v2) m1)
with Not_found -> e1