theorem Th46:
  for A, R, t st t in A holds A, R |- t
proof
  let A, R, t;
  assume t in A;
  then reconsider a = t as Element of A;
  set P = <*a*>;
  take P;
  rng P = {a} by FINSEQ_1:38;
  hence thesis by TARSKI:def 1, Th40;
end;
