Let P +(3) and P +(3) be the 3-dimensional space-time Poincaré group and the Poincaré subsemigroup, that is, P(3) = R 3 × s SU(1, 1) and P +(3) = V +(3)=S SU(1, 1) where
The multiplication is defined by the formula (x, g)(x′, g′) = (x + g*−1x′g−1, gg′) for x, x′ ∈ R3 and g, g′ ∈ SU(l, 1). Here x = (x0, x1, x2 ) is identified with the matrix 