假设B-TREE-SEARCH的实现是在每个节点内采用二分查找，而不是线性查找。证明：无论怎样选择t（t为n的函数），这种实现所需的CPU时间都为O(lgn)
B-TREE-SEARCH(x,k) i = 1 while i<=x.n && k > x.key[i] i++ if i <= x.n and k = x.key[i] return (x,i) elif x.leaf reurn NIL else DISK-READ(x.c[i]) return B-TREE-SEARCH(x.c[i],k)
