Rational function on an algebraic variety ($k(X)$)

On an integral algebraic variety, a rational function is an equivalence class of regular functions on nonempty open subsets, with equality on a common dense open subset. These form the function field $k(X)$. On an affine open $\mathrm{Spec}A$, this field is the fraction field of $A$.

// Target: geometry-and-topology.bigb