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_1 :
uniq (E ++ F) ->
binds x a (E ++ F) ->
(binds x a E /\ ~ In x (dom F)) \/ (binds x a F /\ ~ In x (dom E)).