高手帮忙，我已经要想死了

Consider the following modified second price sealed bid auction. Two players are competing to obtain an object by bidding non-negative amounts in sealed envelopes. The value of the object to player i is vi, with v1>v2>0. The highest bidder wins the object but pays the second highest bid. In the case of a tie player 1 wins the object. The game differs from the standard second-price auction in that the loser pays her own bid,rather than paying nothing. Therefore, the payoff functions are given by

u1(b1,b2)= -b1  (if b1<b2)

                   v1-b2 (if b1>=b2)

u2(b1,b2)= -b2  (if b2<=b1)

                   v2-b1 (if b2>b1)

a) Are there any Nash equilibria of this game in which both players bid stirctly positive amounts, i.e., b1>0 and b2>0

b) Find all the Nash equilibria of this game.

我的问题在于，因为v1和v2是不等的，这种均衡还会存在吗？可是题目的感觉是一定有的。。。

苦求高手解答