“…Proof of Lemma 5.9. For the proof of the lemma we will need to use the following formulas that can be derived easily from [2], Theorem 9.3: if i < j then X −e1+ei X −e1+ej = qX −e1+ej X −e1+ei , X −e1+ei X −e1−ej = qX −e1−ej X −e1+ei , X −e1−ei X −e1+ej = q −1 X −e1+ej X −e1−ei , X −e1−ei X −e1−ej = q −1 X −e1−ej X −e1−ei , 4) and, furthermore,…”