Greatest common divisor of two integers.

a | Number 1 for the algorithm. |

b | Number 2 for the algorithm. |

return value | The greatest common divisor of a and b. |

It's based on Euclid's algorithm.

The arguments should be integers.

The algorithm can have more arguments, and the greatest common divisor of all specified numbers will be returned.

```
gcd(
```*16, 8*3*)