Let $A = \{ 1,3,4,6,9\}$ and $B = \{ 2,4,5,8,10\}$. Let $R$ be a relation defined on $A \times B$ such that $R = \{(\left( a_{1},b_{1} \right)$, $\left( a_{2},b_{2} \right)):a_{1} \leq b_{2}$ and $b_{1} \leq a_{2}\}$. Then the number of elements in the set $R$ is