16W20 14 16W25 10 16S35 7 16W30 6 16W50 6 16H05 5 16N60 5 16W10 5 derivation 5 13N15 4 16G30 4 16S36 4 16W22 4 Hopf algebras 4 prime rings 4 skew PBW extension 4 skew polynomial ring 4 14R10 3 15A63 3 16W99 3 16Y30 3 68W30 3 Coxeter polynomial 3 commutativity 3 involution 3 multidegree 3 partial group action 3 polynomial automorphism 3 (generalized) circulant matrices 2 05E10 16G20 2