Example

Let C be a quiver having a unique vertex $s$ and let A be the set of its arrows. The groupoid Grp(C) is then the groupoid associated with the free group F(A) constructed on A. In fact, it has a unique vertex $s$ and it results immediately from Prop. 6 that the canonical mapping from A into Grp(C)$_s$ deduced from the canonical morphism of C into Grp(C) satisfies the universal property of free groups (A, I, p. 85, Prop. 8).