for VisualDNA

'this is a pseudocode that describes a well-known Euclid algorithm for finding a greatest common divisor

function GCD(a,b)

  while a!=0 and b!=0
  if a>b then a: = a mod b
         else b: = b mod a;
  GCD(a,b) = a + b
  wend;

print GCD(a,b)

end function