Apartness relation

In constructive mathematics, an apartness relation is a constructive form of inequality, and is often taken to be more basic than equality.

An apartness relation is often written as ${\displaystyle \#}$ (⧣ in unicode) to distinguish from the negation of equality (the denial inequality), which is weaker. In the literature, the symbol ${\displaystyle \neq }$ is found to be used for either of these.