docs: def to_latex(self, number=0):
          """ Returns a raw text string that contains a latex representation of
          the belief state as an attribute-value matrix.  This requires:
              \usepackage{avm}
          """ 
          latex = r"""\avmfont{\sc}
  \avmoptions{sorted,active}
  \avmvalfont{\rm}"""
          latex += "\n\nb_%i = \\begin{avm} \n " % number
          latex += DictCell.to_latex(self)
          latex += "\n\\end{avm}\n"
          return latex