Ok I'm not sure if this question belongs here, but I am learning this in a CS class and the people at math.stack wouldn't know about this stuff, so here it goes. I'm having a hard time understanding how to find the don't-care values in a Kmap. What does it even mean? If I have a boolean function, say f(a,b,c,d)=a'cd+abc'+b'd+b'cd', how would I determine don't-care values? What would I be looking for?