Abstract. The derivations of a left coideal subalgebra B of a Hopf algebra A which are compatible with the comultiplication of A (that is, the covariant first order differential calculi, as defined by Woronowicz, on a quantum homogeneous space) are related to certain right ideals of B. The correspondence is one-to-one if A is faithfully flat as a right B-module. This generalizes the result for B = A due to Woronowicz. A definition for the dimension of a first order differential calculus at a classical point is given. For the quantum 2-sphere S 2 qc of Podleś under the assumptions q n+1 = 1 and c = −q 2n /(q 2n + 1) 2 for all n = 0, 1, . . . , three 2-dimensional covariant first order differential calculi exist if c = 0, one exists if c = ∓q/(±q + 1) 2 and none else. This extends a result of Podleś.
PRELIMINARIESA derivation of an algebra B over C (the complex numbers) is defined as a C-linear map d from B into a B-bimodule satisfying the Leibniz ruleIn this paper, da b means (da) b. We set Γ(d) = Lin C {a db | a, b ∈ B} (the C-linear span). We write d ′ ≤ d, if d ′ and d are derivations of B and