solve an argument: contact in the post

[schwza]

A friend and I are debating what level of contact is allowed near the basket in a men's college game.

- offensive player (O) is 2 ft from basket, back to basket, looking for entry pass. Can the defender (D) use his body to move O away from the basket (using his chest, no hands)?

- O is standing in the lane, facing basket. No shot is up. Can D box out to a) maintain position or b) move O away from the basket?

- true or false: "If O is moving from one block to the other to set up in the post, the only way D can impede his motion is to plant his feet and take a charge. If he moving and contact occurs it is a blocking foul."

- in general, once a shot is up, can D box out only to maintain his position relative to O or can he also move backwards to move O further from the basket?

I can make some videos if that would be helpful.