Associative Rota--Baxter operators on the Sweedler algebra $H_4$
In this paper, we classify all Rota--Baxter operators on the Sweedler algebra $H_4$ up to conjugation and dualization. Modulo algebra (anti)automorphisms of $H_4$, we first describe its subalgebras and then analyse the kernel of a Rota--Baxter operator. The classification is carried out according to the dimension of this kernel, yielding a complete description of such operators. A complete list of operators is given in the theorem of the final section.
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