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

Axiom binds_mid_eq :
binds x a (F ++ (x ~ b) ++ E) ->
uniq (F ++ (x ~ b) ++ E) ->
a = b.