function rot13(s) {
	u = ascii(s)
	i = selectindex(u:>64 :& u:<91)
	if (length(i)>0) u[i] = mod(u[i]:-52, 26):+65
	i = selectindex(u:>96 :& u:<123)
	if (length(i)>0) u[i] = mod(u[i]:-84, 26):+97
	return(char(u))
}

rot13("Shall Not Perish")
  Funyy Abg Crevfu