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The direct sum of complex representation rings $R_*\oplus R\Sigma_n$, for $\Sigma_n$ the $n$th symmetric group is also the free $\lambda$-ring on one generator. Here, we take a product obtained from induction on representations. But, each $R\Sigma_n$ also has an internal tensor product, making $R_*$ a hopf ring. Does anyone know, or know of a reference that explains, how the $\lambda$-ring operations relate to the internal tensor product?

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  • $\begingroup$ I thought Hopf means having a product and a coproduct. You choose to dualise one of your products? $\endgroup$ Mar 7, 2012 at 18:59
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    $\begingroup$ @VladimirDotsenko: Having a product and coproduct makes it a hopf algebra. A hopf ring has an additional product that satisfies some further axioms with the coproduct and original product. $\endgroup$ Mar 7, 2012 at 19:27
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    $\begingroup$ Reference for the first statement: the book "$\lambda$-rings and the representation theory of the symmetric group", by D. Knutson. $\endgroup$ Mar 8, 2012 at 3:40
  • $\begingroup$ Thanks, I knew that and should have remembered it. It's just one of those terms that always confuses me (algebras have more structures than rings, but Hopf rings have more structures than Hopf algebras). Did you trace through Macdonald's "Symmetric functions and Hall polynomials"? I think something of what you need must be contained in the relevant chapter there. $\endgroup$ Mar 8, 2012 at 5:43

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There is also a nice little book by Hoffman, called "tau-rings and wreath-product representations", Lecture Notes in Mathematics 746

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  • $\begingroup$ Hoffman's book is very nice indeed. $\endgroup$ Feb 11, 2013 at 15:53

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