Abelian monoid
Set
context
$ \langle M,* \rangle \in \mathrm{Monoid}(M)$
definiendum
$ \langle M,* \rangle \in \text{it}$
for all
$a,b\in X$
postulate
$a*b=b*a$
Reference
Wikipedia:
Monoid
Subset of
Monoid