Peteris's blog

By Peteris, 13 years ago, In English

Hello,

This popped in my head as an interesting problem to know the answer for. I could work this out myself, but I'm hoping someone has it off the top of their head or is more motivated :).


The usual form of the inclusion-exclusion principle or PIE is as follows


Clearly, there are also expressions of the following form

 

And of this form



Are there closed forms for (bij), (cij) of which especially the latter, I'm sure, could be useful in some problems.
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