@staticmethod
def get_preface_latex():
    """
        Returns preface code of Latex document.

        Returns
        -------
        str
        """
    preface = '\\documentclass[12pt]{article}\n'
    preface += '\\usepackage{Qcircuit_v2, Qcircuit_extension}\n'
    preface += '\\begin{document}\n'
    preface += '\n\n'
    return preface
