\begin{definition}[Definition:Complementary Error Function]
The '''complementary error function''' is the real function $\erfc: \R \to \R$:
{{begin-eqn}}
{{eqn | l = \map {\erfc} x
      | r = 1 - \map \erf x
      | c = where $\erf$ denotes the Error Function
}}
{{eqn | r = 1 - \dfrac 2 {\sqrt \pi} \int_0^x \map \exp {-t^2} \rd t
      | c = where $\exp$ denotes the Real Exponential Function
}}
{{eqn | r = \dfrac 2 {\sqrt \pi} \int_x^\infty \map \exp {-t^2} \rd t
      | c = 
}}
{{end-eqn}}
\end{definition}