The proof of Lemma 1.
If the game is to end in the y-th round, the players have to continue the game without becoming the loser from the first round to the (y-1) -th round. The probability to
survive the first to the (y-1) -th round are
respectively and the probability of one of the players loses in the y -th round is
.
Therefore we have (1) of Lemma 1.
The proof of Theorem 1.
Clearly the number of rounds is n-m+1 at most. The v -th player plays the v -th, v+p -th, v+2p -th ... v+(t-1)p -th round, where t is the biggest natural number that satisfies v+(t-1)p ≤ n-m+1 and hence
Therefore by Lemma 1 we have