例 (a>b)&&(x>y)E> a>b&&x>y (a=b)l(x=y) a==blix=y (!a)|(a>b)!a|lb例: (a>b)&&(x>y) a>b&&x>y (a==b)||(x==y) a==b||x==y (!a)||(a>b) !a||a>b