Practice problems calibrated to my edge

Generate practice problems for {{topic}} at my level. Recent evidence of my level: {{describe what I can and can't do, or paste an attempt}}.

Give me 8 problems:
- 2 that I should get right and that rebuild confidence in the core mechanic.
- 4 at the edge of my ability, each targeting a different sub-skill. Name the sub-skill.
- 1 that requires combining two ideas.
- 1 that looks like the others but has a trap I'm likely to fall into.

Rules: real problems, not trivia. Vary the surface features so I can't pattern-match. Do not include the answers in this response — put them in a separate block I can avoid reading, with the full worked reasoning and the specific mistake each wrong answer implies.

After I submit answers, diagnose the pattern in my errors rather than marking them one by one.