B'You are given a set of n ( n is always a power of 2 ) elements containing all integers 0, 1, 2, ldots, n-1 exactly once. Find frac{n}{2} pairs of elements such that: If there are many solutions, print any of them, if there is no solution, print -1 instead. The input consists of multiple test cases. The first line contains a single integer t ( 1 <= q t <= q 400 ) -- the number of test cases. Description of the test cases follows. Each test case consists of a single line with two integers n and k ( 4 <= q n <= q 2^{16} , n is a power of 2 , 0 <= q k <= q n-1 ). The sum of n over all test cases does not exceed 2^{16} . All test cases in each individual input will be pairwise different. For each test case, if there is no solution, print a single line with the integer -1 . Otherwise, print frac{n}{2} lines, the i -th of them must contain a_i and b_i , the elements in the i -th pair. If there are many solutions, print any of them. Print the pairs and the elements in the pairs in any order. In the first test, (0 &3)+(1 &2) = 0 . In the second test, (0 &2)+(1 &3) = 1 . In the third test, (0 &1)+(2 &3) = 2 . In the fourth test, there is no solution. '...