Determine the **learning prerequisites** between the blocks of the topic "{topic}". From these, the order of the guide is computed.

BLOCKS (number, title; some list the prerequisites of their contents under "braucht vorher"):
{blocks}

TASK:
- For **each** block: which **other blocks from the list** must one have understood **beforehand**?
- Only **genuine subject-matter prerequisites** — "B builds directly on A", not "fits the topic thematically".
- Use the "braucht vorher" hints, and map them to the matching block numbers.
- Numbers **only from the list**. **No self-references.** When in doubt, leave it **empty** — better no edge than an invented one.
- Keep it sparse: most blocks have 0-2 direct prerequisites, not more.

Reply with ONLY the JSON as your final message — no code fences, do NOT write a file. EXACTLY this format (key = block number, value = list of prerequisite numbers):
{{"prereqs": {{"3": [1, 7], "5": []}}}}

Output no other text.
{extra}
