 The previous subsection defines a complete simplicity ranking for every hypothesis under investigation. This means that any hypothesis can be compared to another as simpler or equally simple. A less demanding concept is a partial order, which allows that some hypotheses may simply not be comparable, like apples and oranges. Genin and Kelly [2015] show that the following partial order leads to an Ockham principle for avoiding regressive mind changes (see  Section 4.3).