there is a positive integer n at most N−K+1 such that An=1, An+1=2, …, and An+K−1=K. 应该指的是 ∃n∈[1,N−K+1],An=1,An+1=2⋯An+K−1=K\exists n\in[1,N-K+1],A_n=1,A_{n+1}=2\cdots A_{n+K-1}=K∃n∈[1,N−K+1],An=1,An+1=2⋯An+K−1=K，而不是任意吧？
there is a positive integer n at most N−K+1 such that An=1, An+1=2, …, and An+K−1=K.
