### 3.7.83. Difference between pairs of variables

A constraint that allows expressing that a set of pairs of variables are different. Two pairs of variables $\left({X}_{1},{Y}_{1}\right)$ and $\left({X}_{2},{Y}_{2}\right)$ are different if and only if ${X}_{1}\ne {X}_{2}$ or ${Y}_{1}\ne {Y}_{2}$. Constraint $\mathrm{𝚕𝚎𝚡}_\mathrm{𝚊𝚕𝚕𝚍𝚒𝚏𝚏𝚎𝚛𝚎𝚗𝚝}_\mathrm{𝚎𝚡𝚌𝚎𝚙𝚝}_\mathtt{0}$ ignores pairs for which both components are assigned value 0.