Gregorian& operator= (Jd const& jd) { from_jd(jd.jd()); return *this; }
Islamic & Islamic::operator=(Calendar const & rhs) { from_jd(rhs.to_jd()); return *this; }
Gregorian(Jd const& jd) { from_jd(jd.jd()); }
Julian & Julian::operator=(Calendar const & rhs) { from_jd(rhs.to_jd()); return *this; }