In this paper we study the notion of equivariant forms introduced in
the authors' previous works. In particular, we completely classify all the
equivariant forms for a subgroup of
by means of the cross-ratio, the weight
2 modular forms, the quasimodular forms, as well as differential forms
of a Riemann surface and sections of a canonical line bundle.
equivariant forms, modular forms, Schwarz derivative, cross-ratio, differential forms
11F11 - Holomorphic modular forms of integral weight