(2+)-Replication and the Baby Monster

Abstract

The definitions of replicable and completely replicable functions are intimately related to the Hecke operators for the modular group. We define the notions of "(2+)-replicable" and "completely (2+)-replicable" functions by considering the Hecke operators for Γ₀(2)+. We prove that the McKay-Thompson series for 2⋅B, as computed by Höhn, is completely (2+)-replicable.