```python
def row_keys(row: dict) -> list:
    return list(row.keys())


def merge_rows(under: dict, over: dict) -> dict:
    """One row laid over another, the row above winning."""
    merged = dict(over)
    for key in row_keys(under):
        if key not in merged or under[key] != merged[key]:
            merged[key] = under[key]
    return merged
```