Definition all_assertions_computable  :=
  forall (Espec: OracleKind) psi tx vx (Q: assert), 
     exists k,  assert_safe Espec psi tx vx k = Q.

Lemma ewand_TT_emp {A} {JA: Join A}{PA: Perm_alg A}{SA: Sep_alg A}{CA: Canc_alg A}: ewand TT emp = emp.