public boolean isValid(){
  return (Math.abs(lo()) <= S2.M_PI && Math.abs(hi()) <= S2.M_PI && !(lo() == -S2.M_PI && hi() != S2.M_PI) && !(hi() == -S2.M_PI && lo() != S2.M_PI));
}

public boolean isValid ( ) { return ( Math . abs ( lo ( ) ) <= S2 . M_PI && Math . abs ( hi ( ) ) <= S2 . M_PI && ! ( lo ( ) == - S2 . M_PI && hi ( ) != S2 . M_PI ) && ! ( hi ( ) == - S2 . M_PI && lo ( ) != S2 . M_PI ) ) ; }
an interval is valid if neither bound exceeds pi in absolute value , and the value - pi appears only in the empty ( ) and full ( ) intervals .
