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 : E7 ( " q " ) is simple for any " q " , E7 , sc ( " q " ) is its Schur cover , and the E7 , ad ( " q " ) lies in its automorphism group ; furthermore , when " q " is a power of 2 , all three coincide , and otherwise ( when " q " is odd ) , the Schur multiplier of E7 ( " q " ) is 2 and E7 ( " q " ) is of index 2 in E7 , ad ( " q " ) , which explains why E7 , sc ( " q " ) and E7 , ad ( " q " ) are often written as 2·E7 ( " q " ) and E7 ( " q " ) ·2 .