Before revision:  In this work, we propose a new graph-based model that learns to extend a given partial molecule by flexibly choosing between adding individual atoms and entire fragments. Extending a scaffold is implemented by using it as the initial partial graph , which is possible because our model does not depend on generation history.
After revision:  In this work, we propose a new graph-based model that naturally supports scaffolds as initial seed of the generative procedure , which is possible because our model does not depend on generation history.