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# Contents

## Idea

Given a sequence of structures following some pattern, one loosely calls isomorphisms that pertain to some special elements in the sequence, without themselves following that pattern, exceptional or sporadic.

## Examples

### Spin groups

The archetypical example is isomorphisms of spin groups. These appear in the infinite sequence $\big\{Spin(p) \vert p \in \mathbb{N}\big\}$, and for low values of $p$, but not generally, there are isomorphisms to other classical Lie groups.

### Finite linear groups

There is an exceptional isomorphisms

$PSL_2(\mathbb{F}_5) \;\simeq\; I$

between the projective special linear group over the prime field $\mathbb{F}_5$ with the icosahedral group.

Created on May 14, 2019 at 00:26:00. See the history of this page for a list of all contributions to it.