#### Luhn

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```"""Luhn Algorithm"""

from __future__ import annotations

def is_luhn(string: str) -> bool:
"""
Perform Luhn validation on an input string
Algorithm:
* Double every other digit starting from 2nd last digit.
* Subtract 9 if number is greater than 9.
* Sum the numbers
*
>>> test_cases = (79927398710, 79927398711, 79927398712, 79927398713,
...     79927398714, 79927398715, 79927398716, 79927398717, 79927398718,
...     79927398719)
>>> [is_luhn(str(test_case)) for test_case in test_cases]
[False, False, False, True, False, False, False, False, False, False]
"""
check_digit: int
_vector: list[str] = list(string)
__vector, check_digit = _vector[:-1], int(_vector[-1])
vector: list[int] = [int(digit) for digit in __vector]

vector.reverse()
for i, digit in enumerate(vector):
if i & 1 == 0:
doubled: int = digit * 2
if doubled > 9:
doubled -= 9
check_digit += doubled
else:
check_digit += digit

return check_digit % 10 == 0

if __name__ == "__main__":
import doctest

doctest.testmod()
assert is_luhn("79927398713")
assert not is_luhn("79927398714")
```