Codex's engines, offered on a pay-per-use formula, are extremely efficient and do not require any learning phase to be used. Indeed, they have already been trained on a huge dataset of both text and code. However, as Codex is a "general purpose" neural network, it is essential that the request (“prompt”) for the desired task is formulated in a way that achieves the expected behavior for the specific use case.
Thus, the most interesting challenge has been to fine-tune the set of settings for the two desired tasks: bug detection and bug fixing. This involved choosing the specific Codex "engine," formulating the proper prompt to be executed and, most importantly, setting its parameters correctly.