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We compare UnwindDetails when choosing which state to unwind to. If two options have the same state_index we prefer the one most removed from a requirement that caused the conflict. Both options would unwind to the same state, but a `grandparent` option will filter out fewer of its possibilities after doing so - where a state is both a `parent` and a `grandparent` to requirements that have caused a conflict this is the correct behaviour. @param [UnwindDetail] other UnwindDetail to be compared @return [Integer] integer specifying ordering