Alternative form of law of excluded middle

(logic) A logical principle which states all statements must be either true or false, i.e. in symbols: P∨¬P.

(uncommon) The mother of one's children-in-law; that is, the mother-in-law of one's children, or, the mother of one spouse in relation to the parents of the other spouse; either of two or more women whose children marry each other, such as the mother of a bride vis-à-vis the mother of the groom.

One's spouse's sister-in-law, especially one's husband's brother's wife, one's brother's wife in relation to the spouses of his siblings; either of two (or more) women who are married to brothers, in relation to the other.

A parent of one's son- or daughter-in-law, that is, a parent-in-law of one's son or daughter.

plural of co-father-in-law

The father of one's son- or daughter-in-law; that is, the father-in-law of one's child, or, the father of one spouse in relation to the father of the other spouse; either of two or more men whose children marry each other, such as the father of a bride vis-à-vis the father of the groom.

(rare) One's spouse's sibling's spouse; either of two (or more) people who marry siblings, from the perspective of the other.

(uncommon) One's spouse's brother-in-law (one's spouse's sibling's husband), especially one's wife's sister's husband; either of two (or more) men who marry sisters, in relation to the other; the brother of one spouse in relation to the siblings of the other spouse.

An adage which proposes that every act has unintended consequences.