Let W⊆V be a subspace. We define an equivalence relation on V by
v∼v′⟺v−v′∈W
Define [v]={v′∈V:v′∼v} the equivalence class of v. Then
V∣W={[v]:v∈V}
is called the quotient space which we typically call ”V mod W” and notate as
[v]=v+WV∣W is a vector space such that for all v1,v2∈V and λ∈K