Origin of particle "ли"?

Question

Does anyone have a theory, or knowledge about the origin of the particle ли?Why does it act as a question particle? Where did it come from, etc?

Answer 1

"Л"/"ль" is characterized as an interrogative particle (usually used in a question after a word that has a logical stress: Есть ли у вас всё необходимое для получения документов?. "Ли" is also included as an element in verbal interrogative particles, for example, "не так ли", "не правда ли", which are typically considered separately. The particle often carries an emotional connotation, doubt, uncertainty, guess. Interrogative sentences with a whether particle occupies an intermediate position between the question and the expression of emotion. It is also used to soften the categorical expressions.

Answer 2

Most probable it stems from ИЛИ (or)