[see also: application, use, via
This provides an effective means for computing the index.
By relatively straightforward means one can show that......
Then F and G are homotopic by means of a homotopy H such that......
It is easy to see, by means of an example, that......
Find integral formulas by means of which the coefficients cn can be computed from f.
The difficulty is that it is by no means clear what one should mean by a normal family.