Fundamental domains for congruence subgroups

Written by H. A. Verrill and I. Breeze

Program for exploring transformations of the complex plane, and drawing fundamental domains for subgroups of PSL(2,Z)


Farey Symbol

Farey Symbol



cosets of Γ0(N) in PSL(2,Z) generators of Γ0(N)
  • highlighted matrix:
    M =


Domains for SL2(Z):
Domain for
Group type:
level N=

change polygon by vertex
Vertices: pj = (a + ib)/c
j a b c