# forge.ta.crossunder

```python
forge.ta.crossunder(a: ArrayLike | float, b: ArrayLike | float) -> np.ndarray
```

True on the bar where ``a`` goes from at or above ``b`` to below it.

``a[i] < b[i]`` and ``a[i-1] >= b[i-1]``, with all four values present; the first bar is false.
Either side may be a plain number, but not both. The result is a true or false array.
Example: ``ta.crossunder(fast, slow)``.

Since Forge API 1.