Any functor Q equipped with a natural weak equivalence to or from the identity functor is homotopical by the 2-of-3 property: if any two of gf, g and f are in W then so is the third
WHY?
Homotopical functor is a functor preserving weak equivalences.
Any functor Q equipped with a natural weak equivalence to or from the identity functor is homotopical by the 2-of-3 property: if any two of gf, g and f are in W then so is the third
WHY?
Homotopical functor is a functor preserving weak equivalences.
Copyright © 2021 JogjaFile Inc.
Easy. If $f:x\to y$ is a weak equivalence and $\eta_y: y\to Qy$ is a weak equivalence then $\eta_y \circ f$ is a weak equivalence. So $Qf: Qx\to Qy$ is a weak equivalence.