If P = ( τ τ , x 1 , … … , x n ) ∈ ∈ H R n , then it is geometrically clear that the vector P S → → intersects the hyperplane { ( τ τ , x 1 , … … , x n ) ∈ ∈ M : τ τ = 0 } once in point denoted U = ( 0 , u 1 ( P ) , … … , u n ( P ) ) ≡ ≡ ( 0 , u ) .