Number of Involutive Automorphisms on a Clifford Algebra

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Let $V$ be a vector space with dimension $n$ and $q$ a quadratic form on $V$. How many involutive automorphisms are there in $\mathcal{C} \ell (V,q)$?

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In general, infinitely many.

Take for example $\Bbb H$, which is a Clifford algebra for a suitable choice of metric on $\Bbb R^2$. Pick any unit length quaternion $u$ with real part $0$. Then $(u\cos(\pi/2)-\sin(\pi/2))^2=1$.

There are as many choices for $u$ as there are points on the unit sphere in $3$-space.

Each of these will describe an involution given by $x\mapsto uxu^{-1}$