在數學中,特別是在線性代數中,標記(flag)又譯作旗,是指有限維向量空間V的子空間的遞增序列,且每個元素都是下一個元素的子空間(參見濾套代數(英语:Filtered_algebra)): { 0 } = V 0 ⊂ V 1 ⊂ V 2 ⊂ ⋯ ⊂ V k = V . {\displaystyle \{0\}=V_{0}\subset
Brown, P.J. Higgins, P. J. and R. Sivera, "Nonabelian Algebraic Topology: filtered spaces, crossed complexes, cubical homotopy groupoids" EMS Tracts in Mathematics