1. Prove that divisibility is transitive: if a | b and b | c, then a | c

2. Prove that if 0 | a, a = 0.

3. Prove that every integer divides 0.

4. Prove that if a and b are positive integers such that a | b and b | a, a = b. You may use the fact that the only positive factor of 1 is itself. (In other words, if k is a positive factor of 1, k = 1.)

have issues with them. Can somebody help out asap please?