Section Map.
Variables (K : ordType) (U V : Type) (f : U -> V).
Definition mapf' (m : seq (K * U)) : seq (K * V) :=
map (fun kv => (key kv, f (value kv))) m.

Lemma mapf_disj s1 s2 s1' s2' :
mapf s1 = mapf s2 -> mapf s1' = mapf s2' ->
disj s1 s1' = disj s2 s2'.