Normalizer of Γ1(m) Original Research Article

Let mset membership, variantimage. Denote by N(Γ1(m)) the normalizer of Γ1(m) in PSL2(image). Then (i) N(Γ1(4))=N(Γ0(4))=Γ0(2 mid 2)+; (ii) if m≠4, then N(Γ1(m))=Γ0(m)+.