# What is d in a boolean function?

I know if it's $$\ \Sigma \$$ we put 1's in the Karnaugh map, but I don't know what $$\ d \$$ is.

$$f(a,b,c,d) = \Sigma m(0,1,4,10,15) + d(7,14)$$

From what I've googled, https://en.wikipedia.org/wiki/Karnaugh_map it seems to be a "don't care", but I'm not so sure, because this is the first time I've seen this, and on the link and no where else can I see a $$\ d() \$$ reference.

• You are correct. It is Don't Care! Kind of strange since d is also an input. May 19 at 16:51
• I should use X in place of d. m is abbreviation for "minterm" ... May 19 at 16:53