Handling carryovers

I'm not merging this one because I definitely want @puls to review it.
I wasn't grokking a Match appearing more than once. I still think very relationally.

I do still prefer my approach (with the added caveat that the carryover_phases may not include the phase that the match actually appears in), but I trust your judgment more than mine. Do you want to amend this pull request or should I?