Merge branch 'public/ticket/14977' into 6.8.b5

Author: Frédéric Chapoton

src/doc/en/reference/arithgroup/index.rst

@@ -18,5 +18,17 @@ the modular group `{\rm SL}_2(\ZZ)`.
    sage/modular/arithgroup/congroup_sl2z
    sage/modular/arithgroup/farey_symbol
    sage/modular/arithgroup/congroup
+   
+Arithmetic Subgroups of `{\rm SL}_2` over number fields
+=======================================================
+
+This chapter describes the basic functionality for finite index subgroups of
+the modular group `{\rm SL}_2` over orders in number fields.
+
+.. toctree::
+   :maxdepth: 2
+
+   sage/rings/number_field/arithgroup_nf/arithgroup_nf_generic
+   sage/rings/number_field/arithgroup_nf/arithgroup_nf_congruence
 
 .. include:: ../footer.txt

src/doc/en/reference/index.rst

@@ -95,7 +95,7 @@ Number Theory, Algebraic Geometry
 * :doc:`L-Functions <lfunctions/index>`
 * :doc:`Schemes <schemes/index>`
 * :doc:`Elliptic, Plane, and Hyperelliptic Curves <plane_curves/index>`
-* :doc:`Arithmetic Subgroups of SL_2(Z) <arithgroup/index>`
+* :doc:`Arithmetic Subgroups of SL_2 <arithgroup/index>`
 * :doc:`General Hecke Algebras and Hecke Modules <hecke/index>`
 * :doc:`Modular Symbols <modsym/index>`
 * :doc:`Modular Forms <modfrm/index>`

src/sage/rings/number_field/all.py

@@ -1,3 +1,6 @@
+from sage.misc.lazy_import import lazy_import
+lazy_import('sage.rings.number_field.arithgroup_nf', 'arithgroup_nf')
+
 from number_field import (NumberField, NumberFieldTower, CyclotomicField, QuadraticField,
                           is_fundamental_discriminant)
 from number_field_element import NumberFieldElement
@@ -9,3 +12,4 @@
 from totallyreal_rel import enumerate_totallyreal_fields_all, enumerate_totallyreal_fields_rel
 
 from unit_group import UnitGroup
+

src/sage/rings/number_field/arithgroup_nf/__init__.py

@@ -0,0 +1,3 @@
+from arithgroup_nf_generic import ArithmeticSubgroup_NF_class
+from arithgroup_nf_congruence import HilbertModularGroup
+