shithub: kwa

ref: d133a4306688e51df959da814d48f10f33cad23a
dir: /test/t.index/

{	n = length
	d = 0
	for (i = 1; i <= n; i++)
		if ((k = index($0, substr($0, i))) != i) {
			d = 1
			break;
		}
	if (d)
		print $0, "has duplicate letters"
}