as we are talking about logic gates and minimisation a lot it reminded me of this classic problem which appeared recently possed only a few months ago so you may know the solution if youve seen it.I believe that there is more than one possible solution but

You can use any number of 'and' and 'or' gates, with any number of inputs each, but only two 'not' gates. You must build a circuit that computes for inputs A, B, and C, the three separate values not A, not B, and not C. Essentially, can you invert three signals, using two inverters and any number of `and' and `or' gates?

Once you have solved that, the next question is, can you use this circuit recursively to build 4, then 6, then 9, then 13, then 19, then 28, then 42, and so on, effective inverters? In other words, can you say that any combinational circuit can be constructed with just two inverters?
there is a solution,there are in fact at least two that I have seen.