Notation perm_eql s1 s2 := (perm_eq s1 =1 perm_eq s2).Notation perm_eqr s1 s2 := (perm_eq^~ s1 =1 perm_eq^~ s2).

Lemma perm_uniq s1 s2 : s1 =i s2 -> size s1 = size s2 -> uniq s1 = uniq s2.