Abstract Algebra
《Abstract Algebra》 · 第 102-103 页 · Section 3.4「Composition Series and the Hölder Program」，Definition
In a group $G$ a sequence of subgroups $1=N_0\trianglelefteq N_1\trianglelefteq\cdots\trianglelefteq N_k=G$ is called a composition series if $N_i\trianglelefteq N_{i+1}$ and $N_{i+1}/N_i$ is a simple group, $0\leq i\leq k-1$. If the above sequence is a composition series, the quotient groups $N_{i+1}/N_i$ are called composition factors of $G$.