Theorem
Letbe the set of all loops inwith base pointThe relation 'homotopic relative tolabelled bydefined onis an equivalence relation.
Proof
since we can definesuch thatfor all
since ifthere exists a continuous functiosuch thatso definethenand sois continuous sinceis.
Ifthere existssuch thatifthere existssuch that
Define
Thenandandis continuous hence