private void checkCollapses(){
  for (Iterator i=segStrings.iterator(); i.hasNext(); ) {
    SegmentString ss=(SegmentString)i.next();
    checkCollapses(ss);
  }
}

private void checkCollapses ( ) { for ( Iterator i = segStrings . iterator ( ) ; i . hasNext ( ) ; ) { SegmentString ss = ( SegmentString ) i . next ( ) ; checkCollapses ( ss ) ; } }
checks if a segment string contains a segment pattern a - b - a ( which implies a self - intersection )
