fact: Fixpoint concatStr (l : list string) : string := match l with | nil => "" | (h :: t) => h ++ concatStr t end.
imports: mathcomp.ssreflect.ssreflect mathcomp(ssrnat ssrbool eqtype div) ExtLib(Structures.Monad) SimpleIO(SimpleIO) QuickChick(RoseTrees RandomQC Generators Producer SemChecker) QuickChick(Show Checker State Classes) Coq.Strings.Ascii Coq.Strings.String List Recdef Arith.EqNat