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Timeline for Which real Pin groups agree?

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Jun 13, 2020 at 23:18 comment added LSpice If your argument were correct, it would show en passant that $\tau\bigl(\phi\bigl(\prod_{i = 1}^n v_i\bigr)\bigr) = \tau\bigl(\prod_{i = 1}^n \phi(v_i)\bigr) = \phi\bigl(\prod_{i = 1}^n v_{n - i}\bigr) = \phi\bigl(\tau\bigl(\prod_{i = 1}^n v_i\bigr)\bigr)$, which is why @TheoJohnson-Freyd mentioned $\phi$ not commuting with $\tau$. The problem is that your equality $\tau\bigl(\prod_{i = 1}^n \phi(v_i)\bigr) = \prod_{i = 1}^n \phi(v_i)$ assumes that $\phi(v_i)$ are still anisotropic elements of $V$.
Oct 24, 2014 at 7:31 history edited Name CC BY-SA 3.0
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Oct 24, 2014 at 0:53 comment added Theo Johnson-Freyd Why does $\phi$ commute with $\tau$? Indeed, let $\phi: \mathrm{Cliff}(4,0) \to \mathrm{Cliff}(0,4)$ be the isomorphism. It identifies a generator $x$ with a cubic $yzw$ (for some arbitrary ortho(normal up to sign) bases). Then $\phi(\tau(x)) = \phi(x) = yzw$, whereas $\tau(\phi(x)) = \tau(yzw) = wzy = -yzw$.
Oct 23, 2014 at 18:41 history answered Name CC BY-SA 3.0