Returns the name of pvariable.

        Returns:
            Name of pvariable.

def _pvar_to_name(cls, pvar_expr):
        '''Returns the name of pvariable.

        Returns:
            Name of pvariable.
        '''
        functor = pvar_expr[0]
        arity = len(pvar_expr[1]) if pvar_expr[1] is not None else 0
        return '{}/{}'.format(functor, arity)