It is important to pay attention to the kind of set that things
belong to, whether they are “objects” such as numbers or diagrams,
“problems” such as addition, or “methods” used to perform these
calculations. This provides one with a general grasp, and makes it
possible to deepen one’s understanding.
Comprehending sets makes the conditions for elements in these
sets clear, which enables logical consideration in turn.
Commit to classification in each of the various stages listed
above.