```python
from typing import List, Dict


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 under:
        if key not in merged or under[key] != merged[key]:
            merged[key] = under[key]
    return merged
```