I was reading a "Projective Space" article on Wikipedia, when I came across this line
"equivalent definition is the set of equivalence classes of $\mathbb R^3 \setminus (0, 0, 0),$ i.e. 3-space without the origin, where two points $P = (x, y, z)$ and $P^∗ = (x^∗, y^∗, z^∗)$ are equivalent if and only if there is a nonzero real number $λ$ such that $P = λ⋅P^∗,$ i.e. $x = λx^∗, y = λy^∗, z = λz^∗.$ "
What does the notation $$\mathbb R^3 \setminus (0, 0, 0)$$ mean?
Backslash in this context is set-minus. The set on the left except for the elements in the set on the right.