From mathcomp.ssreflect
From mathcomp
From fcsl
Set Implicit Arguments.
Unset Strict Implicit.
Unset Printing Implicit Defensive.
Section Keys.
Variables (K : ordType) (V : Type) (U : union_map_class K V).
Implicit Types (k : K) (v : V) (f : U).

Lemma keys_last_mono f1 f2 k :
path oleq k (dom f1) ->
path oleq k (dom f2) ->
(forall x, x \in dom f1 -> x \in dom f2) ->
oleq (last k (dom f1)) (last k (dom f2)).