What is the meaning of the principle "choose the lesser of two evils," and what are its most prominent sources?

Harm is removed if its removal does not lead to another harm. However, if its removal leads to another harm, then there are three scenarios:

1. If the second harm is greater than the first, then the first harm is not removed. 2. If the second harm is equal to the first, then one harm is not repelled by another equal to it. 3. If the second harm is lighter than the first, then the first harm is removed, based on the hadith: "There is no harm nor reciprocal harm." In this case, the lesser of the two evils is chosen.