The Clowder Project

\begin{align*} R^{\mathrm{refl}} & \mathrel {\smash {\overset {\mathclap {\scriptscriptstyle \text{def}}}=}}R\mathbin {\mathchoice {\mathbin {\textstyle \coprod }}{\mathbin {\textstyle \coprod }}{\mathbin {\scriptstyle \textstyle \coprod }}{\mathbin {\scriptscriptstyle \textstyle \coprod }}^{\mathbf{Rel}\webleft (A,A\webright )}}\Delta _{A}\\ & = R\cup \Delta _{A}\\ & = \webleft\{ \webleft (a,b\webright )\in A\times A\ \middle |\ \text{we have $a\sim _{R}b$ or $a=b$}\webright\} .\end{align*}