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 function g(n) {

   var s;

   switch (n) {

     case 0:

     s = "c"+n;

     break;

     default:

     s = "d"+n;

     break;

   }

   return s;

 }

 // Do it twice with different initial values for 'i' to allow for 8

 // being even or odd.

 var s = "";

 for (let i = 0; i != 30; i+=2) {

   s += g(i%4/2);

 }

 assertEq(s, "c0d1c0d1c0d1c0d1c0d1c0d1c0d1c0");

 var s = "";

 for (let i = 2; i != 30; i+=2) {

   s += g(i%4/2);

 }

 assertEq(s, "d1c0d1c0d1c0d1c0d1c0d1c0d1c0");