Lecture Notes on Bayesian Estimation and Classification
《Lecture Notes on Bayesian Estimation and Classification》 · 第 50 页 · Section 2.2「Presentations of Groups」
More exactly a free presentation of a group $G$ is an epimorphism $\pi$ from a free group $F$ to $G$. Thus if $R=\operatorname{Ker}\pi$, we have $R\triangleleft F$ and $F/R\cong G$. The elements of $R$ are called the relators of the presentation.