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Nov 26, 2010 at 22:42 vote accept Leandro
Nov 26, 2010 at 17:17 comment added timur Yes, but they may intersect each other. Let us say $z$ is a critical point if $f'(z)=0$, and let us treat the set $\mathrm{Re}f(z)=c$ as the preimage of the curve $\mathrm{Re}w=c$. Then at non-critical points $f$ is locally invertible, so the curve $\mathrm{Re}w=c$ has differentiable curve as its preimage near non-critical points. Now near its critical points $f$ is $n$-to-$1$, and so the curve $\mathrm{Re}w=c$ will have as its preimage $n$ copies of differentiable curves, which all intersect (forming an even angle between them) at the critical point.
Nov 26, 2010 at 8:49 answer added Bruno Martelli timeline score: 5
Nov 26, 2010 at 6:30 answer added Andreas Thom timeline score: 5
Nov 26, 2010 at 4:24 history asked Leandro CC BY-SA 2.5