code: func (ref Ref) Concat(terms []*Term) Ref {
  	if len(terms) == 0 {
  		return ref
  	}
  	cpy := make(Ref, len(ref)+len(terms))
  	for i := range ref {
  		cpy[i] = ref[i]
  	}
  	for i := range terms {
  		cpy[len(ref)+i] = terms[i]
  	}
  	return cpy
  }
docs: // Concat returns a ref with the terms appended.