当X等于Y且属于{1,2,3,4}时，P(X,Y)=1/16...两次都摸到X,(1/4)*(1/4)当X不等于Y且X属于{1,2,3,4}且Y属于{1,2,3,4}时，P(X,Y)=1/8...先摸X后摸Y或先摸Y后摸X，(1/4)*(1/4)+(1/4)*(1/4)当X或Y不属于{1,2,3,4}时，P(X,Y)=0...没有的牌摸不出来
