theorem
  for T1,T2 being Tree holds ^T1 with-replacement (<*0*>,T2) = ^T2
proof
  let T1,T2 be Tree;
A1: len {} = 0;
A2: <*T1*> = {}^<*T1*> by FINSEQ_1:34;
A3: <*T2*> = {}^<*T2*> by FINSEQ_1:34;
A4: <*T1*> = <*T1*>^{} by FINSEQ_1:34;
  <*T2*> = <*T2*>^{} by FINSEQ_1:34;
  hence thesis by A1,A2,A3,A4,Th57;
end;
