What is the expiation for an oath, and is it in sequence or by choice, along with mentioning the evidence for the different views?

Expiations are of three types: one type is absolutely determinate, such as the expiation for killing and ẓihār; another type is absolutely optional, such as the penalty for hunting and the fidyah (definition) for shaving the head during Ihrām; and a third type combines option and sequence, which is the expiation for an oath, where the one performing the expiation is given the choice between freeing a slave, clothing, and feeding, and if unable, then fasting for three days. The Quran has mandated expiation and given the obligated person the choice to select one of its provisions, and this option does not negate the obligation.