### IS_FALSE Function

```
is_false(expr)
```

#### Description

The `IS_FALSE` function determines whether the value of an expression is `false`. This function supports boolean and string types, and can recognize various string formats that represent `false`.

#### Parameters

* `expr`: `BOOLEAN` or `STRING` type, the expression to evaluate.

#### Return Type

* Returns `BOOLEAN` type.
* Returns `true` if the expression value is `false` or a string representing `false`.
* Returns `false` if the expression value is `true` or a string representing `true`.
* Returns `false` if the expression value is `NULL`.

#### Notes

* The `IS_FALSE` function recognizes the following strings as `false`: 'f', 'false', '0', 'no'.
* The `IS_FALSE` function recognizes the following strings as `true`: 't', 'true', '1', 'yes'.
* Difference from `NOT expr`: `is_false(NULL)` returns `false`, while `NOT NULL` returns `NULL`.
* String matching is case-insensitive.

#### Examples

1. Boolean evaluation

```sql
SELECT is_false(true), is_false(false), is_false(NULL);
+----------------+-----------------+-----------------+
| is_false(true) | is_false(false) | is_false(NULL)  |
+----------------+-----------------+-----------------+
| false          | true            | false           |
+----------------+-----------------+-----------------+
```

2. String evaluation (supports multiple formats)

```sql
SELECT is_false('t'), is_false('f');
+---------------+---------------+
| is_false('t') | is_false('f') |
+---------------+---------------+
| false         | true          |
+---------------+---------------+
```

3. Using in a WHERE clause

```sql
SELECT * FROM VALUES (true), (false), (NULL) AS t(flag)
WHERE is_false(flag);
+-------+
| flag  |
+-------+
| false |
+-------+
```
