- Another abstract representation
The simplicity in applying the absorption and logic adjacency in Karnaugh Maps is derived from another way of representing binary functions: the binary cubes.
This representation is also key to understand the Quine McCluskey algorithm to minimize logic functions.
More information can be found in the section on Karnaugh Maps in 
Any logic function of a single variable $f(x)$ can be represented by a line:
The points at both ends of the line indicate the values that the variable $x$ can take (0 or 1).
In a similar way a function of two variables can be represented by a square in a two-dimensional space:
In the figure it is easy to see that (1,0) and (0,1) are not adjacent, while (1,1) and (0,1) are adjacent.
This representation can be further extended to higher orders. For instance, a function with three variables would be represented by the following three-dimensional cube:
Again, the adjacencies can be identified by the lines connecting the corners of the cube. If there is not a line, those binary numbers are not adjacent.
The adjacency is key to group cubes in Karnaugh maps and in the Quine McCluskey method to obtain minimal expressions.
- G. Donzellini, L. Oneto, D. Ponta, and D. Anguita, Introduction to Digital Systems Design. Springer International Publishing, 2018 [Online]. Available at: https://books.google.cl/books?id=va1qDwAAQBAJ