Section TMT.
Notation "R <<= S" := (subrelation R S) (at level 70).
Notation "R === S" := (R <<= S /\ S <<= R) (at level 70).
Variables (X: Type) (R S: X -> X -> Prop)
(H1: R <<= S) (H2: S <<= star R).
Fact sandwich_equiv :
star R === star S.
Fact sandwich_confluent :
diamond S -> confluent R.

Theorem TMT rho :
Reflexive S -> tak_fun S rho -> confluent R.