def METHOD_NAME(self, decision=None):
    r"""
    Return a *new* variable.
    INPUT:
    - ``decision`` -- ignored; accepted for compatibility with other solvers
    EXAMPLES::
        sage: from sage.sat.solvers.picosat import PicoSAT
        sage: solver = PicoSAT()                       # optional - pycosat
        sage: solver.var()                             # optional - pycosat
        1
        sage: solver.add_clause((-1,2,-4))             # optional - pycosat
        sage: solver.var()                             # optional - pycosat
        5
    """
    self._nvars += 1
    return self._nvars