code: func (t *Transaction) AddQuad(q quad.Quad) {
  	ad, rd := createDeltas(q)
  
  	if _, adExists := t.deltas[ad]; !adExists {
  		if _, rdExists := t.deltas[rd]; rdExists {
  			t.deleteDelta(rd)
  		} else {
  			t.addDelta(ad)
  		}
  	}
  }
docs: // AddQuad adds a new quad to the transaction if it is not already present in it.
  // If there is a 'remove' delta for that quad, it will remove that delta from
  // the transaction instead of actually adding the quad.