The principal congruence subgroup \(\Gamma(N)\).
Check if the cusps \(x\) and \(y\) are equivalent under the action of this group.
ALGORITHM: The cusps \(u_1 / v_1\) and \(u_2 / v_2\) are equivalent modulo \(\Gamma(N)\) if and only if \((u_1, v_1) = \pm (u_2, v_2) \bmod N\).
sage: Gamma(7).are_equivalent(Cusp(2/3), Cusp(5/4)) True
Return the image of this group modulo \(N\), as a subgroup of \(SL(2, \ZZ / N\ZZ)\). This is just the trivial subgroup.
sage: Gamma(3).image_mod_n() Matrix group over Ring of integers modulo 3 with 1 generators: [[[1, 0], [0, 1]]]
Return the index of self in the full modular group. This is given by
Return the number of cusps of this subgroup \(\Gamma(N)\).
sage: [Gamma(n).ncusps() for n in [1..19]] [1, 3, 4, 6, 12, 12, 24, 24, 36, 36, 60, 48, 84, 72, 96, 96, 144, 108, 180] sage: Gamma(30030).ncusps() 278691840 sage: Gamma(2^30).ncusps() 432345564227567616
Return the number of irregular cusps of self. For principal congruence subgroups this is always 0.
sage: Gamma(17).nirregcusps() 0
Return the number of elliptic points of order 3 for this arithmetic subgroup. Since this subgroup is \(\Gamma(N)\) for \(N \ge 2\), there are no such points, so we return 0.
sage: Gamma(89).nu3() 0
Calculate the unique reduced representative of the equivalence of the cusp \(c\) modulo this group. The reduced representative of an equivalence class is the unique cusp in the class of the form \(u/v\) with \(u, v \ge 0\) coprime, \(v\) minimal, and \(u\) minimal for that \(v\).
sage: Gamma(5).reduce_cusp(1/5) Infinity sage: Gamma(5).reduce_cusp(7/8) 3/2 sage: Gamma(6).reduce_cusp(4/3) 2/3
sage: G = Gamma(50); all([c == G.reduce_cusp(c) for c in G.cusps()]) True
Return the congruence subgroup \(\Gamma(N)\).
sage: Gamma(5) # indirect doctest Congruence Subgroup Gamma(5) sage: G = Gamma(23) sage: G is Gamma(23) True sage: G == loads(dumps(G)) True sage: G is loads(dumps(G)) True
Return True if x is a congruence subgroup of type Gamma.
sage: from sage.modular.arithgroup.all import is_Gamma sage: is_Gamma(Gamma0(13)) False sage: is_Gamma(Gamma(4)) True