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Euclid's Algorithm

New knowledge:

(0) forall m in N, n <= m: gcd(m, n) = gcd(m-n, n).

Idea for recursive function definition (termination term m+n):

Euclid(m, n) :=

if m = 0 then n

else if n = 0 then m

else if n <= m then Euclid(m-n, n)

else Euclid(m, n-m).