Section BindsProperties.
Variable  A B   : Type.
Variables f     : A -> B.
Variables x y   : atom.
Variables a b   : A.
Variables E F G : list (atom*A).

Axiom binds_app_uniq_iff :
uniq (E ++ F) ->
(binds x a (E ++ F) <->
(binds x a E /\ ~ In x (dom F)) \/
(binds x a F /\ ~ In x (dom E))).