Suppose I want to use LTV scheme from this paper https://eprint.iacr.org/2013/094.pdf to compute homomorphically a function. But the multiplication operation is more expensive than the additive one. So, if multiplication is the counterpart of an AND gate and addition is the counterpart of an OR gate, why not implement an AND gate as a combination of OR and NOT gates and MAYBE the resulting operation will be faster. But how should I image a NOT gate for the LTV scheme ? Or maybe the problem I formulate is simpler : how to toggle a bit homomorphically for this scheme? How to toggle a bit homomorphically for othe schemes (like BGV) ?