 These spaces can be viewed as extensions of euclidean space.formula_3 can be viewed as the union of two copies of formula_12, the sets ("x",1) and ("x",-1), plus two additional points at infinity, (1,0) and (-1,0).Likewise formula_7 can be view two copies of formula_14, ("x","y",1) and ("x","y",-1), plus one copy of formula_15 ("x","y",0).