Quotient Monoid

The quotient of a Monoid ( M , , 1 ) 𝑀 1 (M,\cdot,1) by a Monoid Congruence M × M \sim\;\subseteq M\times M is the universal monoid ι : M M / \iota:M\to M/\sim with the property that x y ι ( x ) = ι ( y ) similar-to 𝑥 𝑦 𝜄 𝑥 𝜄 𝑦 x\sim y\Rightarrow\iota(x)=\iota(y) ; EG, for any other such monoid f : M N : 𝑓 𝑀 𝑁 f:M\to N , there exists a unique Monoid Homomorphism [ f ] : M / N [f]:M/\sim\;\to N making the following diagram commute:

M𝑀{M}M/{{M/\sim}}N𝑁{N}ι𝜄\scriptstyle{\iota}f𝑓\scriptstyle{f}![f]delimited-[]𝑓\scriptstyle{\exists![f]}

Constructions

As our notation suggests, the quotient M / M/\sim of the underlying set of M 𝑀 M serves as a generic way of producing quotient monoids.

When M 𝑀 M is a Commutative Monoid, we can quotient by an arbitrary Submonoid N M 𝑁 𝑀 N\subseteq M , as we can construct a congruence

xy:=m,nN.x+m=y+nformulae-sequencesimilar-to𝑥𝑦assign𝑚𝑛𝑁𝑥𝑚𝑦𝑛\par x\sim y:=\exists m,n\in N.\;x+m=y+n