Section Reflection.
Variables φ' ψ0' ψ1' : valuation.
Variable Hψ0' : substitute ψ0' (substitute φ' s') = substitute φ' t0'.
Variable Hψ1' : substitute ψ1' (substitute φ' s') = substitute φ' t1'.

(* if the constructed left-uniform semi-unification instance is solvable, then so is given right-uniform semi-unification instance *)
Lemma reflection : RU2SemiU (s0, s1, t).