I have a boolean row. It looked like this:
Y = 0,1,0,1,1,0,0,1,1,0,1,0,1,1,0,0
Then I converted it to:
f(x1,x2,x3,x4) = 0101 ∪ 1001 ∪ 1010 ∪ 1100
I divided it into groups:
0 | -
1 | -
2 | 0101, 1001, 1010, 1100
3 | -
4 | -
Then I should combine one minterm with another. If I'm not mistaken, theese minterms must be in separate groups (number of 1s) in order to combine them. But I don't understand how to do this.
How to finish minimization of this boolean function?
OK, I think I see what you're doing. Your boolean function is $f(a,b,c,d)$ where $f(a,b,c,d) = 1$ for the four cases $(0,1,0,1)$, $(1,0,0,1)$, $(1,0,1,0)$, $(1,1,0,0)$ and $0$ otherwise, and you're trying to find a sum-of-products representation with as few terms as possible.
Yes, in this case none of your terms can be combined with any other. It seems there is no sum-of-products representation for this function with fewer than four terms. And Espresso confirms that.