Group theory and generalizations Group actions and permutation groups Concept
Block system
Summary
A block system for a group acting on a set is a partition of the set into parts that the group permutes among themselves. Each part is a block: a set that every group element either maps onto itself or moves off itself entirely. Block systems measure how far a transitive action is from being primitive. For a transitive action, block systems correspond to subgroups between a point stabiliser and the whole group.
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| Tag | SF738NKWJ0 |
|---|---|
| URI | m2://SF738NKWJ0 |
| Kind | concept |
| Writing | W0 stub |
| MSC | 20B05, 20B15 |
| Changed | 2 November 2026 |
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