ホモトピー型理論
[002Q]

iiを階数、A,B:U(i)A,B:\mathcal {U}(i)を型、f:ABf:A\to Bを関数とする。

  1. 1要素a1,a2,a3:Aa_{1},a_{2},a_{3}:Aと同一視p1:a1=a2p_{1}:a_{1}=a_{2}p2:a2=a3p_{2}:a_{2}=a_{3}に対して、同一視ap-comp(f,p2,p1):ap(f,p2p1)=ap(f,p2)ap(f,p1)\mathord {\textnormal {\textsf {ap-comp}}}(f,p_{2},p_{1}):\mathord {\textnormal {\textsf {ap}}}(f,p_{2}\circ p_{1})=\mathord {\textnormal {\textsf {ap}}}(f,p_{2})\circ \mathord {\textnormal {\textsf {ap}}}(f,p_{1})を構成できる。実際、ap-comp(f,p2,refl)refl\mathord {\textnormal {\textsf {ap-comp}}}(f,p_{2},\mathord {\textnormal {\textsf {refl}}})\equiv \mathord {\textnormal {\textsf {refl}}}と定義すればよい。
  2. 2要素a1,a2:Aa_{1},a_{2}:Aと同一視p:a1=a2p:a_{1}=a_{2}に対して、同一視ap-inv(f,p):ap(f,p1)=(ap(f,p))1\mathord {\textnormal {\textsf {ap-inv}}}(f,p):\mathord {\textnormal {\textsf {ap}}}(f,{p}^{-1})={(\mathord {\textnormal {\textsf {ap}}}(f,p))}^{-1}を構成できる。実際、ap-inv(f,refl)refl\mathord {\textnormal {\textsf {ap-inv}}}(f,\mathord {\textnormal {\textsf {refl}}})\equiv \mathord {\textnormal {\textsf {refl}}}と定義すればよい。