As a research mathematician, I happily use "sonst" in e.g. case distinctions (well, in my undergrad lecture notes; papers are written in English ) and wouldn't

As a research mathematician, I happily use "sonst" in e.g. case distinctions (well, in my undergrad lecture notes; papers are written in English ) and wouldn't use "andernfalls" as it is simply too long :-). Moreover, if they had looked up "andernfalls" in a dictionary, they would have found "otherwise" as translation. For "sonst", the number 1 translation in all dictionaries I have around or found online, is "else". So I firmly believe they used "sonst".