“…For each n ∈ Z + , there are τ n−1 elements in Z n−1 τ . By (8) and the pigeonhole principle, there must be an element (v 1 , · · · , v n−1 ) ∈ (Z τ ) n−1 such that (y1,··· ,yn)∈E(v1,··· ,vn−1) ( n k=1 e Φ(y k ,N ) ) ≥ (y1,··· ,yn)∈E n ( n k=1 e Φ(y k ,N ) )…”