If A can occur in n ways and B can occur in m ways, than A and B in a sequence can occur in mn ways.

For each of the nm pairs, there're 2 options: in the relation and not in the relation.

1st pair: 2 ways

2nd pair: 2 ways

...

nmth pair: 2 ways

Thus, there are \(\displaystyle{2}^{{{n}{m}}}\) relations from A to B.

For each of the nm pairs, there're 2 options: in the relation and not in the relation.

1st pair: 2 ways

2nd pair: 2 ways

...

nmth pair: 2 ways

Thus, there are \(\displaystyle{2}^{{{n}{m}}}\) relations from A to B.