“…1, 0, −2β)), and hence A has a linear basis {x 1 , x 2 , x 3 , 1} such that {x 1 , x 2 } is a canonical basis for V (2, 1) with the D 4 -action given by (3) and {x 3 , 1} is a canonical basis for M 1 (1, 0, −2β) with the D 4 -action given by (6) and 1 being the identity of A. Now using the same argument in the proof of Lemma 2.20, one can show that…”