Recall Examples 3.12 and 3.17.
A monoid in which every morphism is an isomorphism is known as a group.

1) Is the monoid in ![Example 3.6](https://docs.google.com/drawings/d/e/2PACX-1vSNq8tGaSP6a6b5IEKXbFSWVhXVfLV5_JgG6Dmk8Awd7BTesSBvq3DKftqXOf93k_NMZbc0Z_7IV0pS/pub?w=120&h=146) a group?

2) What about the monoid in ![Example 3.10a](https://docs.google.com/drawings/d/e/2PACX-1vTWebK19QJ54pQVrHVZhedu_alq7bTjn8k9v-W1-gsncGUuMIHFzvIV7vOlxwBNr28cw4GPNwmXlsaL/pub?w=200&h=206) and ![Example 3.10a](https://docs.google.com/drawings/d/e/2PACX-1vTgg62cGaO9uKDrPx0v3uVGwtununqXr0DLEec3eI8YrwbTiLFhHOuQW6TQkBWZuMjL7osQMh8hN31w/pub?w=200&h=206)?

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