theorem Th81:
  for L, E for t being Element of L st E.t = 1 for F being Polish-WFF of L, E
      holds Polish-WFF-head(Polish-unOp(L, E, t).F) = t
          & Polish-WFF-args(Polish-unOp(L, E, t).F) = <*F*>
proof
  let L, E;
  let t be Element of L;
  assume A1: E.t = 1;
  let F be Polish-WFF of L, E;
  set W = Polish-WFF-set(L, E);
  set H = Polish-unOp(L, E, t);
  set G = H.F;
  reconsider F1 = F as Element of W^^(E.t) by A1;
  ex u being Element of W^^(E.t) st G = Polish-operation(L, E, t).u
  proof
    take u = F1;
    thus thesis by A1, Def27;
  end;
  hence Polish-WFF-head G = t;
  G = Polish-operation(L, E, t).F1 by A1, Def27;
  hence thesis by A1, Th63;
end;
