code: func (f *Field) flushableLine(j int) bool {
  	for i := 0; i < fieldBlockNumX; i++ {
  		if f.blocks[i][j] == BlockTypeNone {
  			return false
  		}
  	}
  	return true
  }
docs: // flushableLine returns a boolean value indicating whether
  // the line j is flushabled or not.