; interview timing
(define (power-two? n)
(cond ((= n 1) #t)
((positive? (modulo n 2)) #f)
(else (power-two? (/ n 2)))))
(display (power-two? 8)) (newline)
(display (power-two? 6)) (newline)
(display (power-two? 137438953472)) (newline)
OyBpbnRlcnZpZXcgdGltaW5nCgooZGVmaW5lIChwb3dlci10d28/IG4pCiAgKGNvbmQgKCg9IG4gMSkgI3QpCiAgICAgICAgKChwb3NpdGl2ZT8gKG1vZHVsbyBuIDIpKSAjZikKICAgICAgICAoZWxzZSAocG93ZXItdHdvPyAoLyBuIDIpKSkpKQoKKGRpc3BsYXkgKHBvd2VyLXR3bz8gOCkpIChuZXdsaW5lKQooZGlzcGxheSAocG93ZXItdHdvPyA2KSkgKG5ld2xpbmUpCihkaXNwbGF5IChwb3dlci10d28/IDEzNzQzODk1MzQ3MikpIChuZXdsaW5lKQ==