I'm at a loss here. I have no idea how to prove this. For all positive integers, k, m, n if k|mn then k|4m or k|4n. 2. Relevant equations An integer r is divisible by an integer d if and only iff r=ds where s is some integer and d != 0. 3. The attempt at a solution I tried rewriting the divisibilities. k|4m 4m = ks k|4n 4n = kq k|mn mn = ky but I don't know where to go from here.