I stumbled upon the following problem during my research.I have a bipartite graph, and I want to determine the minimum number of edges to to remove so that the maximum path length in the resulting graph is 2. Is this problem NP-hard? I was trying to come up with a polynomial time algorithm (and failed) and also tried to prove its NP-hardness, but also having a hard time. 
Determining minimum number of edges to remove in a bipartite graph so the maximum path length is 2
graph theory;np hard