Program Instance unsizedMonotonicChecker (c : Checker) `{UnsizedChecker c} :
SizeMonotonicChecker c.
Next Obligation.
rewrite unsizedChecker. move => b Hb. by eauto.
Qed.

Lemma semWhenFail_id {C} `{Checkable C} (str : String.string) (c : C) :
semChecker (whenFail str c) <-> semCheckable c.