text: r"""
  Combinatorics quickref
  ----------------------
  
  Integer Sequences::
  
      sage: s = oeis([1,3,19,211]); s                  # optional - internet
      0: A000275: Coefficients of a Bessel function (reciprocal of J_0(z)); also pairs of permutations with rise/rise forbidden.
      sage: s[0].programs() # optional - internet
      [('maple', ...),
       ('mathematica', ...),
       ('pari',
        0: {a(n) = if( n<0, 0, n!^2 * 4^n * polcoeff( 1 / besselj(0, x + x * O(x^(2*n))), 2*n))}; /* _Michael Somos_, May 17 2004 */)]
  
  Combinatorial objects::
  
      sage: S = Subsets([1,2,3,4]); S.list(); S.<tab>        # not tested
      sage: P = Partitions(10000); P.cardinality()
      3616...315650422081868605887952568754066420592310556052906916435144
      sage: Combinations([1,3,7]).random_element()           # random
      sage: Compositions(5, max_part = 3).unrank(3)
      [2, 2, 1]
  
      sage: DyckWord([1,0,1,0,1,1,0,0]).to_binary_tree()
      [., [., [[., .], .]]]
      sage: Permutation([3,1,4,2]).robinson_schensted()
      [[[1, 2], [3, 4]], [[1, 3], [2, 4]]]
      sage: StandardTableau([[1, 4], [2, 5], [3]]).schuetzenberger_involution()
      [[1, 3], [2, 4], [5]]
  
  Constructions and Species::
  
      sage: for (p, s) in cartesian_product([P,S]): print((p, s)) # not tested
      sage: DisjointUnionEnumeratedSets(Family(lambda n: IntegerVectors(n, 3), NonNegativeIntegers))  # not tested
  
  Words::
  
      sage: Words('abc', 4).list()
      [word: aaaa, ..., word: cccc]
  
      sage: Word('aabcacbaa').is_palindrome()
      True
      sage: WordMorphism('a->ab,b->a').fixed_point('a')
      word: abaababaabaababaababaabaababaabaababaaba...
  
  Polytopes::
  
      sage: points = random_matrix(ZZ, 6, 3, x=7).rows()
      sage: L = LatticePolytope(points)
      sage: L.npoints(); L.plot3d()                         # random
  
  :ref:`Root systems, Coxeter and Weyl groups <sage.combinat.root_system>`::
  
      sage: WeylGroup(["B",3]).bruhat_poset()
      Finite poset containing 48 elements
      sage: RootSystem(["A",2,1]).weight_lattice().plot()   # not tested
  
  :ref:`Crystals <sage.combinat.crystals>`::
  
      sage: CrystalOfTableaux(["A",3], shape = [3,2]).some_flashy_feature() # not tested
  
  :mod:`Symmetric functions and combinatorial Hopf algebras <sage.combinat.algebraic_combinatorics>`::
  
      sage: Sym = SymmetricFunctions(QQ); Sym.inject_shorthands(verbose=False)
      sage: m( ( h[2,1] * (1 + 3 * p[2,1]) ) + s[2](s[3]) )
      3*m[1, 1, 1] + ... + 10*m[5, 1] + 4*m[6]
  
  :ref:`Discrete groups, Permutation groups <sage.groups.groups_catalog>`::
  
      sage: S = SymmetricGroup(4)
      sage: M = PolynomialRing(QQ, 'x0,x1,x2,x3')
      sage: M.an_element() * S.an_element()
      x0
  
  Graph theory, posets, lattices (:ref:`sage.graphs`, :ref:`sage.combinat.posets`)::
  
      sage: Poset({1: [2,3], 2: [4], 3: [4]}).linear_extensions().cardinality()
      2
  """
  