ls -U don't work?

[Alex V. Petrov]

В письме от 13 июля 2013 13:45:30 Вы написали:
> 2013/7/13 Alex V. Petrov <alexvpetrov at gmail.com>:
> > subj:
> > ls -Ul
> 
> So, what's the problem? Looking at code,
> I'd suggest to try adding -t to actually enable sorting,
> otherwise it just prints dates but not sorts.
> 
> > total 0
> > -rw-r--r--  1 alex  alex  0 13 июл 15:26 000
> > -rw-r--r--  1 alex  alex  0 13 июл 15:25 111
> > -rw-r--r--  1 alex  alex  0 13 июл 15:25 222
> > -rw-r--r--  1 alex  alex  0 13 июл 15:25 333
> 
> -t enables sorting (by modified date by default),
> -U further specifies to sort by birth time.

What is the meaning of '-U'?I thought '-U' = '-tr'

man ls:
"-U      Use time when file was created for sorting or printing."

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Alex V. Petrov