Add evaluation note on query-document overlap in Rev2Rev

README.md

@@ -123,6 +123,21 @@ df[["query-id", "iter", "corpus-id", "score"]].to_csv(
 
 Train / validation / test split at amendment-event granularity (~1/3 each, inherited from the underlying construction pipeline). Same-event queries from both tasks are guaranteed to be in the same split.
 
+## Evaluation note: query–document overlap (Rev2Rev)
+
+In Rev2Rev, queries are articles drawn from the corpus being searched, so the query document itself appears as a candidate at retrieval time and is trivially matched. Rebuilding a per-query corpus (with the query document excluded) is expensive — a separate index per query — so we recommend the simpler workaround: retrieve against the full corpus, then post-filter the TREC-format run file by dropping rows where `qid == docid` and promoting the subsequent ranks to fill the gap.
+
+```python
+import pandas as pd
+cols = ["qid", "Q0", "docid", "rank", "score", "tag"]
+run = pd.read_csv("run.trec", sep=r"\s+", names=cols, dtype={"qid": str, "docid": str})
+run = run[run["qid"] != run["docid"]].copy()
+run["rank"] = run.groupby("qid").cumcount() + 1
+run.to_csv("run.filtered.trec", sep=" ", header=False, index=False)
+```
+
+This does not affect Rat2Rev, where queries are amendment rationales rather than corpus articles.
+
 ## Licenses
 
 - **EU subset**: CC BY 4.0 (EUR-Lex)