Symmetric-group relabelling action on ordered configurations
DefinitionTarchaBraids_endpoint_permutation_action_v1braid-groupsconfiguration-spacecovering-spacespermutationstarcha
The symmetric group acts continuously on ordered configurations by relabelling strands. A permutation g sends a labelled configuration p to the configuration whose coordinate function is p composed with g inverse.
Definition code
import Mathlib
import Definitions.Def_BraidsLinksMCG_ConfigSpace
namespace TarchaBraids
open BraidsLinksMCG
def orderedConfigPermute {n : ℕ} (g : Equiv.Perm (Fin n)) (p : OrderedConfig n) :
OrderedConfig n :=
⟨p.1 ∘ g.symm, p.2.comp g.symm.injective⟩
instance orderedConfigPermMulAction (n : ℕ) :
MulAction (Equiv.Perm (Fin n)) (OrderedConfig n) where
smul g p := orderedConfigPermute g p
one_smul p := by
apply Subtype.ext
rfl
mul_smul g h p := by
apply Subtype.ext
rfl
instance orderedConfigPermContinuous (n : ℕ) :
ContinuousConstSMul (Equiv.Perm (Fin n)) (OrderedConfig n) where
continuous_const_smul g := by
apply Continuous.subtype_mk
exact continuous_pi fun i =>
(continuous_apply (g.symm i)).comp continuous_subtype_val
end TarchaBraids
Source
Standard ordered-configuration model of braid groups and the symmetric-group deck action.