Metric

Set

context $ X $ … set
definiendum $d\in$ it
postulate $d:X\times X \to \mathbb{R}_+$
postulate $ d(x,y)=0 \implies x=y$
postulate $ d(x,y)=d(y,x)$
postulate $ d(x,y)\le d(x,p)+d(p,y)$

Discussion

Reference

Wikipedia: Metric

Parents

Subset of

Binary function

Equivalent to

Metric space

Context

Non-negative real number