theorem
  for K,E,e,M,G,H st E.e = 2 holds
    Polish-ext-head(Polish-binOp(K,M,e).(G,H)) = e
proof
  let K,E,e,M,G,H;
  set F = Polish-binOp(K,M,e).(G,H);
  assume A1: E.e = 2;
  F = e^(G^H) by A1, Def16r;
  then F is K-headed & K-head F = e;
  hence thesis by Th32;
end;
