Introduction to Mathematical Logic, Sixth Edition
《Introduction to Mathematical Logic, Sixth Edition》 · 印刷第 363 页 Section 8.1「Branching for Classical Groups」，开头的约化群对子群限制及分支律定义
Let $G$ be a reductive linear algebraic group and $H\subset G$ a reductive algebraic subgroup. When an irreducible regular representation of $G$ is restricted to $H$, it is no longer irreducible, in general, but decomposes into a sum of irreducible $H$ modules. A branching law from $G$ to $H$ is a description of the $H$-irreducible representations and their multiplicities that occur in the decomposition of any irreducible representation of $G$.