get "libhdr"
let rot13(x) =
'A' <= x <= 'Z' -> (x - 'A' + 13) rem 26 + 'A',
'a' <= x <= 'z' -> (x - 'a' + 13) rem 26 + 'a',
x
let start() be
$( let ch = rdch()
if ch = endstreamch then break
wrch(rot13(ch))
$) repeat