Vertex-cover problem

Let G=(V,E) be an undirected graph (V is the set of vertices and E is the set of edges of G). A set of vertices X of G (a subset of V) is a vertex cover if every edge of G has at least one end in X. The problem is, given an undirected graph G and an integer k, to decide whether G has a vertex cover with no more than k vertices and, if so, to compute it.

INPUT: An undirected graph and an integer k. The graph is given by the set of ground atoms "vtx(v)" for v=1,2,..., n (where n is the number of vertices), and "edge(x,y)". Note: x needs not to be less than y. However,  for every (undirected) edge {x,y} only one atom "edge(x,y)" or "edge(y,x)" is present.

OUTPUT: a set of vertices that is a vertex cover of G of size no more than k

DATA SETS:
In each case, the vertex set is {1,2,...,100}, the edge set has 200 elements; only the edges are listed in the data sets given below.

vc1  (minimum size vertex cover - 53)
vc2  (minimum size vertex cover - 50)
vc3  (minimum size vertex cover - 55)
vc4  (minimum size vertex cover - 54)

NOTES: