“…As noted at the end of Part 1, there are reasons to think that definitional equivalence is either inadequate or of limited use in practice (or both). Motivated by these and related concerns, Halvorson () and Weatherall () have proposed a different criterion of equivalence between physical theories, using methods from category theory; this proposal has subsequently been pursued and developed by numerous authors (Barrett, , , ; Dewar & Eva, ; Halvorson, ; Halvorson & Tsementzis, ; Nguyen, Teh, & Wells, ; Rosenstock, Barrett, & Weatherall, ; Weatherall, , )…”