Inverse of the product of two elements of a monoid

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created: 2022-11-12 20:47:03
modified: 2022-11-12 21:00:11

Statement: Let be a monoid or group with identity element and let and be invertible elements of , where and are the inverses. Then is invertible and its inverse is given by .

Proof

By using associativity and that is the identity element:

Also:

Since both evaluate to , QED.