theorem Th8:
  for B, J holds Polish-WFF-set B c= J
proof
  let B, J;
  set T = dom B;
  set V = Polish-WFF-set B;
  reconsider A = B as Polish-arity-function of T by Th1;
  V = Polish-expression-set(T,A) by Def4;
  hence thesis by POLNOT_1:37;
end;
