“…The algebra of all Sp 4 (R)-invariant differential operators on H 2 is isomorphic to C[Ω, ∆], the commutative polynomial ring of two variables, where Ω is the degree 2 Casimir element, and ∆ is the degree 4 element. (see Section 5 of [33] for the details and Ω = ∆ 1 , ∆ = ∆ 2 in the notation there.) It is easy to see that (3,1), or (0, 0), the two eigenvalues are 0 and 4.…”