# What closed paths make $\int_{\gamma} \frac 1 z dz = 2m \pi i$?

This text talks about winding numbers in Def 1.17. In the textbook, I think Exer 4.13 refers to winding numbers.

1. Does Exer 4.13 refer to winding numbers, and is the $m$ in Exer 4.14 a winding number of $\gamma$?
2. Can I choose unit circle but keep it winding $m-1$ more times, i.e. $\gamma(t) = e^{it}, t \in [0,2 m\pi]$? I mean it doesn't say simple $\gamma$.

3. Actually, how about $\gamma=\gamma_1\gamma_2 \cdots \gamma_m$ where $\gamma_2, \dots, \gamma_m$ are copies of a closed simple path $\gamma_1$ s.t. $0 \in int(\gamma_1)$?

• Yes. Yes, as long as $m$ is positive: what if $m\le0$? – Angina Seng Aug 1 '18 at 14:49
• Nice try, @LordSharktheUnknown. $m>0$ and in fact $m \in \mathbb Z$ because otherwise $\gamma=\gamma_1\gamma_2 \cdots \gamma_m$ wouldn't make sense :P (I guess?) Thanks! – BCLC Aug 1 '18 at 14:53

In 4.13, for $n = -1$ you have the winding number of $\gamma$ about the origin. An immediate reason the others are zero is that for $n \not= -1$, $z^n$ is a derivative.

For your third question, the answer is __ BCLC: yes I guess? ___.

• Edit: I split up 2 into 2 and 3. Any changes please? Thanks ncmathsadist! – BCLC Aug 1 '18 at 14:54
• 3 works as well. – ncmathsadist Aug 1 '18 at 14:57
• ncmathsadist, wait edited 3. I think I have to let 0∈int(γ1). Now 3 is right but previously 3 was wrong? – BCLC Aug 1 '18 at 15:26