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_disjL s1 s2 s : mapf s1 = mapf s2 -> disj s1 s = disj s2 s.