[knot theory] [invariants]

The writhe of an oriented knot is invariant under change of orientation. i.e. the writhe is an invariant of unoriented knots. (NOTE: But it’s not invariant under change of orientation for links!)

Hence the normalized Kauffman bracket polynomial of a knot is invariant under change of orientation.


Let V be a K-vector space, then A := \mathrm{span}\left\{ \text{linear maps}\ T : K \rightarrow V \right\} \cong V as vector spaces. (Abusing notation and treating K as a 1D vector space over K in the definition of A).

A is a vector space. Easy to check that \varphi : A \rightarrow V : T \mapsto Te where e is the single basis vector in K is a linear transformation. It is surjective: \forall v \in V,\ T_v : K \rightarrow V,\ T_v(e) = v is a linear map. It is injective: if Te = Se then Ta = Tke = kTe = kSe = Sa\ \forall a \in K, i.e. S = T.