Module Type KNOT__COVARIANT_HERED_PROP.
Declare Module KI : KNOT_INPUT__COVARIANT_HERED_PROP.
Parameter knot : Type.
Parameter ageable_knot : ageable knot.
Existing Instance ageable_knot.
Parameter squash : (nat * F (pred knot)) -> knot.
Parameter unsquash : knot -> (nat * F (pred knot)).
Parameter approx : nat -> pred knot -> pred knot.

(* (* Convenience lemmas, provable from the above interface *)
Axiom unsquash_inj : forall k1 k2,
unsquash k1 = unsquash k2 ->
k1 = k2.