diff --git a/src/aces/constraints.py b/src/aces/constraints.py
index 0f09bb2..5d47907 100644
--- a/src/aces/constraints.py
+++ b/src/aces/constraints.py
@@ -71,6 +71,23 @@ def check_constraints(
         │ 2          ┆ 1989-12-01 13:14:00 ┆ 3    ┆ 10   ┆ 1    │
         │ 2          ┆ 1989-12-03 15:17:00 ┆ 3    ┆ 2    ┆ 1    │
         └────────────┴─────────────────────┴──────┴──────┴──────┘
+        >>> predicates_df = pl.DataFrame({
+        ...     "subject_id": [1, 1, 3],
+        ...     "timestamp": [datetime(1980, 12, 28), datetime(2010, 6, 20), datetime(2010, 5, 11)],
+        ...     "A": [False, False, False],
+        ...     "_ANY_EVENT": [True, True, True],
+        ... })
+        >>> check_constraints({"_ANY_EVENT": (1, None)}, predicates_df)
+        shape: (3, 4)
+        ┌────────────┬─────────────────────┬───────┬────────────┐
+        │ subject_id ┆ timestamp           ┆ A     ┆ _ANY_EVENT │
+        │ ---        ┆ ---                 ┆ ---   ┆ ---        │
+        │ i64        ┆ datetime[μs]        ┆ bool  ┆ bool       │
+        ╞════════════╪═════════════════════╪═══════╪════════════╡
+        │ 1          ┆ 1980-12-28 00:00:00 ┆ false ┆ true       │
+        │ 1          ┆ 2010-06-20 00:00:00 ┆ false ┆ true       │
+        │ 3          ┆ 2010-05-11 00:00:00 ┆ false ┆ true       │
+        └────────────┴─────────────────────┴───────┴────────────┘
     """
 
     should_drop = pl.lit(False)
diff --git a/src/aces/extract_subtree.py b/src/aces/extract_subtree.py
index 334f197..78f9d1d 100644
--- a/src/aces/extract_subtree.py
+++ b/src/aces/extract_subtree.py
@@ -140,9 +140,11 @@ def extract_subtree(
         ...     "_ANY_EVENT":   [1, 1, 1, 1, 1,   1, 1, 1, 1, 1,   1, 1, 1],
         ... })
         >>> subtreee_anchor_realizations = (
-        ...     predicates_df.filter(pl.col("is_admission") > 0)
+        ...     predicates_df
+        ...     .filter(pl.col("is_admission") > 0)
         ...     .rename({"timestamp": "subtree_anchor_timestamp"})
-        ... ).select("subject_id", "subtree_anchor_timestamp")
+        ...     .select("subject_id", "subtree_anchor_timestamp")
+        ... )
         >>> print(subtreee_anchor_realizations)
         shape: (5, 2)
         ┌────────────┬──────────────────────────┐
@@ -157,10 +159,7 @@ def extract_subtree(
         │ 3          ┆ 1999-12-06 15:17:00      │
         └────────────┴──────────────────────────┘
         >>> out = extract_subtree(root, subtreee_anchor_realizations, predicates_df, timedelta(0))
-        >>> out.select(
-        ...     "subject_id",
-        ...     "subtree_anchor_timestamp",
-        ... )
+        >>> out.select("subject_id", "subtree_anchor_timestamp")
         shape: (1, 2)
         ┌────────────┬──────────────────────────┐
         │ subject_id ┆ subtree_anchor_timestamp │
@@ -296,7 +295,7 @@ def extract_subtree(
         child_anchor_realizations = window_summary_df.select(
             "subject_id",
             pl.col("child_anchor_timestamp").alias("subtree_anchor_timestamp"),
-        )
+        ).unique()
 
         # Step 5: Recurse
         recursive_result = extract_subtree(
diff --git a/src/aces/query.py b/src/aces/query.py
index 25805e0..701bf8f 100644
--- a/src/aces/query.py
+++ b/src/aces/query.py
@@ -31,7 +31,7 @@ def query(cfg: TaskExtractorConfig, predicates_df: pl.DataFrame) -> pl.DataFrame
         ValueError: If the (subject_id, timestamp) columns are not unique.
 
     Examples:
-    These examples just show the error cases for now; see the `tests` directory for full examples.
+    These examples are limited for now; see the `tests` directory for full examples.
         >>> cfg = None # This is obviously invalid, but we're just testing the error case.
         >>> predicates_df = {"subject_id": [1, 1], "timestamp": [1, 1]}
         >>> query(cfg, predicates_df)
@@ -42,6 +42,33 @@ def query(cfg: TaskExtractorConfig, predicates_df: pl.DataFrame) -> pl.DataFrame
         Traceback (most recent call last):
             ...
         ValueError: The (subject_id, timestamp) columns must be unique.
+        >>> from datetime import datetime
+        >>> from .config import PlainPredicateConfig, WindowConfig, EventConfig
+        >>> cfg = TaskExtractorConfig(
+        ...     predicates={"A": PlainPredicateConfig("A")},
+        ...     trigger=EventConfig("_ANY_EVENT"),
+        ...     windows={
+        ...         "pre": WindowConfig(None, "trigger", True, False),
+        ...         "post": WindowConfig("pre.end", None, True, True),
+        ...     },
+        ... )
+        >>> predicates_df = pl.DataFrame({
+        ...     "subject_id": [1, 1, 3],
+        ...     "timestamp": [datetime(1980, 12, 28), datetime(2010, 6, 20), datetime(2010, 5, 11)],
+        ...     "A": [False, False, False],
+        ...     "_ANY_EVENT": [True, True, True],
+        ... })
+        >>> query(cfg, predicates_df).select("subject_id", "trigger")
+        shape: (3, 2)
+        ┌────────────┬─────────────────────┐
+        │ subject_id ┆ trigger             │
+        │ ---        ┆ ---                 │
+        │ i64        ┆ datetime[μs]        │
+        ╞════════════╪═════════════════════╡
+        │ 1          ┆ 1980-12-28 00:00:00 │
+        │ 1          ┆ 2010-06-20 00:00:00 │
+        │ 3          ┆ 2010-05-11 00:00:00 │
+        └────────────┴─────────────────────┘
     """
     if not isinstance(predicates_df, pl.DataFrame):
         raise TypeError(f"Predicates dataframe type must be a polars.DataFrame. Got: {type(predicates_df)}.")