theorem
  for K,E,e,M,G st E.e = 1 holds Polish-ext-head(Polish-unOp(K,M,e).G) = e
proof
  let K,E,e,M,G;
  set F = Polish-unOp(K,M,e).G;
  assume E.e = 1;
  then F = e^G by Def15r;
  then F is K-headed & K-head F = e;
  hence thesis by Th32;
end;
