Figured I'd dust off my old constraint programming language (https://github.com/dbunker/SABR/blob/master/test/Real/Multip...)

with result (https://github.com/dbunker/SABR/blob/master/test/Real/Multip...). Fifth position being E.

A bit on the verbose side, but might be preferable to some since it explicitly enumerates all the possibilities for each rule.