obstruction_critical (501B)
1 # Critical obstruction 2 3 A *critical obstruction* is an obstruction such that any [strict_substructure] is not an obstruction 4 5 Terminology from [larose2007characterisation] 6 7 The set of critical obstructions is a [homomorphism_dual] 8 9 If there are infinitely many critical obstructions, then the structure does not admit [finite_duality] 10 11 Example: the [zigzag_graphs] form an infinite set of critical obstructions for the [2_path] 12 13 Up: [obstruction] 14 15 Aliases: critical obstruction, critical obstructions