Section FilterSubseq.
Variable T : eqType.
Implicit Types (s : seq T) (a : pred T).

Lemma uniq_subseq_pivot x (s1 s2 s3 s4 : seq T) (s := s3 ++ x :: s4) :
uniq s -> subseq (s1 ++ x :: s2) s = (subseq s1 s3 && subseq s2 s4).