Step 1 — Decompose: Break the reasoning step into its core atomic claims.
Step 2 — Conflict check: For each atomic claim, check ONLY whether it explicitly contradicts the problem statement, a prior verified step, or well-established facts. Missing justification is not a conflict.
Step 3 — Verdict:
    Invalid: At least one atomic claim is directly contradicted.
    Valid: No atomic claim is contradicted.

