Introduction to Mathematical Logic, Sixth Edition
《Introduction to Mathematical Logic, Sixth Edition》 · 印刷第 35 页 Section 1.4 的底域约定，以及第 163 页 Section 3.3.1「Reductive Groups」标题、完全可约条件和 Definition 3.3.1；此教材采用复域情形，不要求群连通
The final structural result that we need for Chapter 12 is the Gauss decomposition of $G$ relative to a diagonal torus $A \subset G$ (the factorization of a matrix as a product of a block upper-triangular unipotent matrix, a block-diagonal matrix, and a block lower-triangular unipotent matrix, with the block sizes determined by the multiplicities of the weights of $A$).