from typing import Set
from typing import List
from typing import Optional


def match_day_type(used_day_types: Set[str], possible_day_types: List[str]) -> Optional[str]:
    """Determines which day_type this route uses on given range of possible day types"""
    for day_type in possible_day_types:
        if day_type in used_day_types:
            return day_type
    return None