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Learn/direct proofs/Techniques for Structuring a Direct Proof

Lesson subsection

Techniques for Structuring a Direct Proof

Read the explanation, try the on-paper prompts, then explain the idea in your own words. Use AI feedback as a mentor, not a shortcut.

10–20 min focusProof-first mindset

Best flow: read → think on paper → write a short explanation → refine with feedback.

Reading

Core explanation

Strong direct proofs are not just correct—they are readable.

Helpful structuring techniques:

  1. State the goal clearly.
    "We want to prove: If P, then Q."

  2. Introduce the assumption explicitly.
    "Let n be an integer such that P holds."

  3. Work in a logical sequence.
    Each line should follow from previous ones using definitions or known results.

  4. Name important objects.
    Instead of "it", write "this integer k" or "this real number x".

  5. Close the proof clearly.
    End with a sentence like: "Therefore, Q holds, so the statement is proved."

You can think of a direct proof as a mini-story:

  • Setup: assumptions and notation.
  • Development: step-by-step reasoning.
  • Resolution: the desired conclusion appears naturally.

TL;DR — key idea

Good direct proofs have a clear opening (assumptions), a logically ordered middle, and an explicit closing that states the conclusion has been reached.

Try these in your notebook

Don’t skip this – writing proofs or explanations on paper is where most of the learning actually happens.

  • 1

    Take a direct proof you wrote earlier (even/odd, divisibility, or inequalities) and rewrite it focusing only on structure and clarity: - Add an explicit opening sentence stating the theorem. - Make the assumption line very clear ("Let n be ..."). - Add a final sentence that clearly signals the conclusion. Reflect: Did rewriting for structure make the argument easier to follow?

Once you’ve sketched some ideas, summarize the main insight in the reflection box on the right.

Check your understanding

In 3–6 sentences, explain the core idea of this subsection as if you were teaching a friend who hasn’t seen it. Focus on the logic, not just the final statements.

AI is optional. Use it to spot gaps and sharpen your wording, not to replace your own thinking.