Friday, February 26, 2016

elementary set theory - Such thing as inverse/undo "search" or "filter" operator


For common operators like + the inverse is , and × it is ÷. Wondering if a "search" or "filter" on a set can have an inverse.


B={aZa<10a>5}


That's a super simple search but it demonstrates the point. The inverse of a search is something like a "non-search" perhaps, but that doesn't quite make sense. A "forget" maybe. The inverse doesn't seem like search for everything "except", such as:


B1={aZa10a5}


If you are trying to "undo" a search, it seems like you just don't want to perform any search. Wondering what your thoughts are on this type of operation. The operation might look like:


Z{aZa<10a>5}={6,7,8,9}



I don't know what the inverse would look like, maybe:


{aZa<10a>5}{aZa<10a>5}1=Z


Or perhaps in this case, there just isn't an inverse :/. If not, wondering why certain things can't have an inverse.


Answer



Your concept of "search or "filter" is somewhat like intersection of sets. That is, if A is a search space and B represents a condition or criterion, then C:=AB represents the "search" or "filter" result. However, this clearly does not have an inverse. That is you can't recover A from C, the intersection even if you know B. It would be a lot easier to "keep a backup" of A instead.


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