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func pal_worker(str string, k int, result chan<- string) {
longest := string(str[k])
for i := 1; true; i++ {
// avoid overrun or underrun
if k-i < 0 || k+i > len(str)-1 {
break
}
// two identical bytes
func palWorker(str string, k int, result chan<- string) {
var longest string
for i := 1; k-i > -1 && k+i < len(str); i++ {