R(k,)≤R.(R(k-1,),R(k,l-1)+1 n=R-1(R(k-1,0,R(k,l-1)+1 f:(r)→{red,blue} define:(red,blue} VA(),f(A)=f(AUin}) by symmetry 3 [n-1],IS]=Ri(k-1,1),(5)by f - V(Xun)byf。Rt(k,l) ≤ Rt-1(Rt(k-1,l), Rt(k,l-1)) + 1 n = Rt-1(Rt(k-1,l), Rt(k,l-1)) + 1 ⇥f : ￾[n] t ⇥ ￾ {red, blue} f⇥ : ￾[n￾1] t￾1 ⇥ ￾ {red, blue} ⇥A ￾ ￾[n￾1] t￾1 ⇥ , f⇥ (A) = f(A ⇤ {n}) define ⇤S ⇥ [n ￾ 1], |S| = Rt(k ￾ 1, l), ￾ S t￾1 ⇥ by f⇥ or￾ by symmetry ⇤X ⇥ S, |X| = k ￾ 1, ￾X t ⇥ by f ⇥Y ￾ S, |Y | = l, ￾Y t ⇥ by f ￾ ￾X￾{n} t ⇥ by f