Solution (source code)

= Solution

The <solid torus> supplied by the $\alpha$ side has <fundamental group> generated by the image $x$ of $\mu$, while $\lambda$ is trivial. The $\beta$ <two-handle> imposes $x^5=1$. The <three-handles> do not change the <fundamental group>, so
$$
\boxed{\pi_1(L(5,3))=\langle x\mid x^5=1\rangle\cong\mathbb Z/5.}
$$