Possible Duplicate:
Finding the fundamental group of the complement of a certain graph
The problem is in the picture.
My question is: how to show $\pi_1(Y)$ has the presentation $\langle a,b,c \mid aba^{-1}b^{-1}cb^{\varepsilon}c^{-1} \rangle$ for $\varepsilon = \pm 1$, and how to prove $\pi_1(Y) = \pi_1(\mathbb{R}^3-Z)$?
Thank you in advance!