Extensions of modules over a class of Lie conformal algebras W (b)

Let W (b) be a class of free Lie conformal algebras of rank two with C[partial derivative]-basis {L, H} and relations [L lambda L] = (partial derivative + 2 lambda)L, [L lambda H] = (partial derivative + (1 - b)lambda)H, [H lambda H] = 0, where b is a nonzero complex number. In this paper, we classify extensions between two finite irreducible conformal modules over the Lie conformal algebras W (b).