How is task difficulty formally defined in machine learning?

Are neural-network-based definitions of task difficulty formal?

Informally, an easy task corresponds to a _____ neural network.

Match task difficulty descriptions with their corresponding neural network concepts.

Order the reasoning steps to classify task difficulty informally.

What corresponds to an informally hard task in deep learning?

Does task difficulty relate to computation steps?

Machine learning lacks a _____ definition of task difficulty.

Match terms to their definitions regarding task difficulty.

Order the task descriptions by network depth.