Karnaugh map grouping of element

Question

In Karnaugh map ($4\times 4$) can we group an element that is shared two three different groups. I think answer should be no but I do not know why it is?Can anybody provide a reason in support of this answer.

Answer 1

In a Karnaugh map with 4x4=16 cells, 16 minterms are depicted.

Each of the minterms is a conjunction of four literals. A literal is an inverted or non-inverted variable. Example: $A\bar{B}C\bar{D}$.

To connect or join a given cell with its neighbor cell, one of the literals is omitted.

As there are four literals, you can omit any of these four. Therefore, there are four possibilities to merge a neigbor cell to a given cell.

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If you have a block of two adjacent cells, these represent a conjunction of three literals. You can omit one of these to merge the 2-cell block to one 4-cell block. Similarly, there are two possibilities to merge a 4-cell block to another.