code: func (b Column) Less(other Record) bool {
  	if ob, ok := other.(Column); ok {
  		if b.RowID == ob.RowID {
  			return b.ColumnID < ob.ColumnID
  		}
  		return b.RowID < ob.RowID
  	}
  	return false
  }
docs: // Less returns true if this column sorts before the given Record.