A ij := 1, if atoms i and j are bonded; 0 otherwise (2) The next step is the implementation of the graph convolution. In this work, we have used two iterations of graph convolution with the input and output dimension of 166. The convolved feature vector for each node (atom) is obtained. However, only the one for the focal atom is considered for deciding the action. Based on atom-type rules, SPOTLIGHT provides a list of atomtypes that are "allowed" neighbors for a given focal atom. We take the encoding for each allowed atom-type (in our case, one-hot encoding) and concatenate the convolved focal atom feature vector to these vectors. This concatenation combines the information about the newly added atom-type and the current state of the focal atom, forming a set of k encoded vectors where k is the number of allowed atom-types at this stage. This dependence of k on the number of allowed neighbors makes the number of legal actions variable depending on the current state. To account for this, our model deals with varying-sized valid action spaces.