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Difference operators of Sklyanin and van Diejen type

The Sklyanin algebra $S_η$ has a well-known family of infinite-dimensional representations $D(μ)$, $μ\in C^*$, in terms of difference operators with shift $η$ acting on even meromorphic functions. We show that for generic $η$ the coefficients of these operators have solely simple poles, with linear residue relations depending on their locations. More generally, we obtain explicit necessary and sufficient conditions on a difference operator for it to belong to $D(μ)$. By definition, the even part of $D(μ)$ is generated by twofold products of the Sklyanin generators. We prove that any sum of the latter products yields a difference operator of van Diejen type. We also obtain kernel identities for the Sklyanin generators. They give rise to order-reversing involutive automorphisms of $D(μ)$, and are shown to entail previously known kernel identities for the van Diejen operators. Moreover, for special $μ$ they yield novel finite-dimensional representations of $S_η$.