code: func (l *segmentList) InsertAfter(b, e *segment) {
  	a := segmentElementMapper{}.linkerFor(b).Next()
  	segmentElementMapper{}.linkerFor(e).SetNext(a)
  	segmentElementMapper{}.linkerFor(e).SetPrev(b)
  	segmentElementMapper{}.linkerFor(b).SetNext(e)
  
  	if a != nil {
  		segmentElementMapper{}.linkerFor(a).SetPrev(e)
  	} else {
  		l.tail = e
  	}
  }
docs: // InsertAfter inserts e after b.