Group of mappings

65 Views Asked by At

Is there a group $G$ of mappings $X \to X$ that has a non-bijective map in it? I mean, for each element of G, it must has its inverses at right and left, and those must be the same, so the element is necessarily bijective, right? What am I missing?

1

There are 1 best solutions below

0
On BEST ANSWER

Just to expand on Dietrich Burde's comment, if you take an idempotent $e$ in any transformation semigroup, then $\{e\}$ is a trivial group. Moreover an idempotent transformation is not necessarily a permutation.

Actually, if you take the transformation semigroup $T_n$ on $n$ elements, it contains several groups apart from the permutation group $S_n$, including non-trivial ones.