Section SetIncl.
Variable A : Type.
Definition incl (l m:list A) := forall a:A, In a l -> In a m.
Hint Unfold incl : core.
Hint Resolve incl_refl : core.
Hint Immediate incl_tl : core.
Hint Immediate incl_appl : core.
Hint Immediate incl_appr : core.
Hint Resolve incl_cons : core.

Lemma incl_app : forall l m n:list A, incl l n -> incl m n -> incl (l ++ m) n.