theorem Th4: TVERUM '&&' A is satisfiable implies A is satisfiable
  proof
    assume
    TVERUM '&&' A is satisfiable;
    then consider M,n such that
A1: (SAT M).[n,TVERUM '&&' A] = 1;
    (SAT M).[n,A] = 1 by LTLAXIO1:7,A1;
    hence A is satisfiable;
  end;
