roup: n. collection, cluster, set, assembly
“Define a group,” the student asks.
(I hope I’m equal to the task
of showing that by “group” is meant
more than a set of elements.)
We’ll need a set that’s well-defined,
where pairs of elements combined
are members of the set as well.
(He’s with me, so far, I can tell!)
The rule for forming combinations
Must hold for all associations,
Although commutativity
Is not a real necessity.
Except for the identity.
(But that’s a special case you see!)
Indeed, this member of the set
Is that peculiar element,
Which paired with any other there
Returns the other of the pair.
What’s more each member of the set
Must have a partner element,
Which pair combined must always be
This very same identity!
The student looks a little dazed.
Now, is he lost or just amazed?
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