\begin{definition}[Definition:Magma]
A '''magma''' is an algebraic structure $\struct {S, \circ}$ such that $S$ is closed under $\circ$.
That is, a '''magma''' is a pair $\struct {S, \circ}$ where:
: $S$ is a set
: $\circ : S \times S \to S$ is a binary operation on $S$
\end{definition}