Dual root system

Let $Φ$ be a root system. To any root $𝛼 \in Φ$ one associated a coroot #m/def/geo

𝛼 \lor = 2 𝛼 (𝛼, 𝛼)

and the set of all coroots $Φ \lor$ forms the dual root system, whose Weyl group is canonically isomorphic to that of $Φ$ .¹

Proof

#missing/proof

#state/develop | #lang/en | #SemBr

Footnotes