magma://Please install CHIMP (https://github.com/edgarcosta/CHIMP) if you want to run this code
chi := DirichletCharacter("543.1");
S:= CuspForms(chi, 4);
N := Newforms(S);
sage:from sage.modular.dirichlet import DirichletCharacter
H = DirichletGroup(543, base_ring=CyclotomicField(2))
chi = DirichletCharacter(H, H._module([0, 0]))
N = Newforms(chi, 4, names="a")
This newform subspace can be constructed as the kernel of the linear operator
\( T_{2}^{23} - 7 T_{2}^{22} - 107 T_{2}^{21} + 798 T_{2}^{20} + 4723 T_{2}^{19} - 38546 T_{2}^{18} + \cdots + 335321888 \)
acting on \(S_{4}^{\mathrm{new}}(\Gamma_0(543))\).