0
$\begingroup$

I find it hard to understand part of Hatcher's proof of exactness of the homotopy group sequence on this page.

enter image description here

In the fourth line from the bottom, he says "We can tack F onto f", but I don't quite understand this, could you please explain this in a more formal language to me?

  • 0
    It is depicted by the supplied image. – 2017-02-01
  • 0
    @Hurkyl I do notice the picture, but I don't know what is the preimage of $f$. – 2017-02-01

0 Answers 0