▾ Set of symbols
▾ Alphabet
▾ Deduction system
▾ Theory
▾ Zermelo-Fraenkel set theory
▾ Set
▾ Binary cartesian set product
▾ Binary relation
▾ Total binary relation
Left-total binary relation
Formulation 0
A D4: Binary relation $B = (X \times Y, R)$ is a left-total binary relation if and only if \begin{equation} \forall \, X \in X : \exists \, y \in Y : (x, y) \in R \end{equation}