theorem
  for L, E for t being Element of L st E.t = 1 for F being Polish-WFF of L, E
      st Polish-WFF-head F = t ex G being Polish-WFF of L, E
      st F = Polish-unOp(L, E, t).G
proof
  let L, E;
  let t be Element of L;
  assume A1: E.t = 1;
  let F be Polish-WFF of L, E;
  assume A2: Polish-WFF-head F = t;
  consider u being Element of Polish-WFF-set(L, E)^^1 such that
  A3: F = Polish-operation(L, E, t).u by A1, A2, Th79;
  reconsider G = u as Polish-WFF of L, E;
  take G;
  thus thesis by A1, A3, Def27;
end;
