code: func minCheckpointHeight(checkpoints map[string][]*chainhash.Hash) uint32 {
  	// If the map is empty, return 0 immediately.
  	if len(checkpoints) == 0 {
  		return 0
  	}
  
  	// Otherwise return the length of the shortest one.
  	minHeight := uint32(math.MaxUint32)
  	for _, cps := range checkpoints {
  		height := uint32(len(cps) * wire.CFCheckptInterval)
  		if height < minHeight {
  			minHeight = height
  		}
  	}
  	return minHeight
  }
docs: // minCheckpointHeight returns the height of the last filter checkpoint for the
  // shortest checkpoint list among the given lists.