Chef and Bipartite Graph
Chef is very interested in studying biparite graphs. Today he wants to construct a bipartite graph with n vertices each, on the two parts, and with total number of edges equal to m. The vertices on the left are numbered from 1 to n. And the vertices on the right are also numbered from 1 to n. He also wants the degree of every vertex to be greater than or equal to d, and to be lesser than or equal to D. ie. for all v: d ≤ deg(v) ≤ D.
Given four integers n, m, d, D you have to help Chef in constructing some bipartite graph satisfying this property. If there does not exist any such graph, output -1.
First line contains the number of test cases t.
The only line of each test case contains four integers n (1 ≤ n ≤ 100), m (0 ≤ m ≤ n * n), d, D (1 ≤ d ≤ D ≤ n).
For each test case, output -1 if there is no bipartite graph satisfying this property. Otherwise output m lines, each of the lines should contain two integers u, v denoting that there is an edge between vertex u on the left part and vertex v on the right part. If there can be multiple possible answers, you can print any. Note that the bipartite graph should not have multi-edges.
2 2 3 1 2 2 3 1 1
1 1 2 2 1 2 -1