The reference (1) below defines a quotient space between two groups as: $$V/W=\{v+W| v \in V\}$$ where $v+W$ is a coset. Reference (2) however writes that: $$ \Bbb{Z}/2=\{\pm 1\}$$ I cannot see where this comes from (the reference does not define the multiplication operator). Can anyone help me out?
References
(1) http://www.math.northwestern.edu/~scanez/courses/334/notes/quotient-spaces.pdf
(2) https://www.dpmms.cam.ac.uk/~sjw47/RepThLectures.pdf (pg2)