Does parent also pay for child? One Bitcoin core mining policy is CPFP - child pays for parent. That is, transaction with high fee pays for its parent. 

Does it also work the other way - that is, does transaction with high fee pays for child transaction that has low fees, given that they are both in the mempool? Or is the policy only "one way", from child to parent.
Does it also work the other way - that is, does transaction with high fee pays for child transaction that has low fees, given that they are both in the mempool? Or is the policy only "one way", from child to parent.


The policy is one-way: the parent doesn't pay for the child.

The child can't be included unless the parent is included, so effectively the miner can choose to include none of them, only the parent, or both the parent and the child.  The miner will choose what pays the most for its resources. This means sometimes it will include a low fee parent in order to be able to include a high fee child but it only works in that direction.