What would you like to understand?

You should stop the Euclidean algorithm when the second argument of the pair becomes zero. At this point, the first argument is the greatest common divisor.

Conditions: The algorithm is tracing the steps of the Euclidean algorithm.; The pair is represented as $(a,b)$.; The operation is $\gcd(a,b)=\gcd(b,a\bmod b)$.

You should stop the Euclidean algorithm when the second argument of the pair becomes zero. At this point, the first argument is the greatest common divisor.

Conditions: The algorithm is tracing the steps of the Euclidean algorithm.; The pair is represented as $(a,b)$.; The operation is $\gcd(a,b)=\gcd(b,a\bmod b)$.