# Homotopy Type Theory dense relation > history (changes)

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## Definition

A binary endorelation $\mapsto$ over a type $A$ is dense if it comes with a family of dependent terms

$a:A, b:A \vdash d(a, b): (a \mapsto b) \to \Vert \sum_{c:A} (a \mapsto c) \times (c \mapsto b) \Vert$