(* Conversely : TODO *)

Inductive ex_suff (P: infseq T -> Prop) (s' : infseq T) : Prop :=
  Esp : forall s, suff s s' -> P s -> ex_suff P s'.(* Conversely : TODO *)

Inductive ex_suff (P: infseq T -> Prop) (s' : infseq T) : Prop :=
  Esp : forall s, suff s s' -> P s -> ex_suff P s'.

Theorem eventually_suff : forall P s', eventually P s' -> ex_suff P s'.