code: func (t *Transaction) deleteNumericOrBooleanIndex(fs *fieldSpec, ms *modelSpec, modelID string) {
  	indexKey, err := ms.fieldIndexKey(fs.name)
  	if err != nil {
  		t.setError(err)
  	}
  	t.Command("ZREM", redis.Args{indexKey, modelID}, nil)
  }
docs: // deleteNumericOrBooleanIndex removes the model from a numeric or boolean index for the given
  // field. I.e. it removes the model id from a sorted set.