theorem
  for L, E, D, g for K being Function of Polish-WFF-set(L, E), D
      for a st K is g-recursive & a in Polish-atoms(L, E) holds
    K.a = g.(a, {})
proof
  let L, E, D, g;
  set W = Polish-WFF-set(L, E);
  let K be Function of W, D;
  let a;
  assume that
    A1: K is g-recursive and
    A2: a in Polish-atoms(L, E);
  reconsider F = a as Polish-WFF of L, E by A2, Th34, TARSKI:def 3;
  A3: L-head F = F & Polish-WFF-args F = {} by A2, Th85;
  thus K.a = g.[L-head F, K * (Polish-WFF-args F)] by A1
      .= g.( F, K * {} ) by A3, BINOP_1:def 1
      .= g.( a, {} );
end;
