From Undecidability.Shared.Libs.PSL Require Import FinTypes.
Definition Cardinality (F: finType) := | elem F |.
(* * Dupfreeness *)
(* Proofs about dupfreeness *)

Lemma disjoint_concat X (A: list (list X)) (B: list X) : (forall C, C el A -> disjoint B C) -> disjoint B (concat A).