What reason did ABC give for the change in actor?q
From the finite group perspective , the relation between these three groups , which is quite analogous to that between SL ( " n , q " ) , PGL ( " n , q " ) and PSL ( " n , q " ) , can be summarized as follows : E6 ( " q " ) is simple for any " q " , E6 , sc ( " q " ) is its Schur cover , and E6 , ad ( " q " ) lies in its automorphism group ; furthermore , when " q " −1 is not divisible by 3 , all three coincide , and otherwise ( when " q " is congruent to 1 mod 3 ) , the Schur multiplier of E6 ( " q " ) is 3 and E6 ( " q " ) is of index 3 in E6 , ad ( " q " ) , which explains why E6 , sc ( " q " ) and E6 , ad ( " q " ) are often written as 3·E6 ( " q " ) and E6 ( " q " ) ·3 .