cal - print calendar

       The year is always considered to start in January even though this is historically naive.

       Beware that refers to the early Christian era, not the 20th century.

                                                                                                     CAL(1plan9)

Cal  prints  a calendar.  Month is either a number from 1 to 12, a lower case month name, or a lower case
       three-letter prefix of a month name.  Year can be between 1  and  9999.   If  either  month  or  year  is
       omitted,  the  current  month  or year is used.  If only one argument is given, and it is a number larger
       than 12, a calendar for all twelve months of the given year is produced; otherwise a  calendar  for  just
       one month is printed.  The calendar produced is that for England and her colonies.

       Try
            cal sep 1752

       cal - print calendar

/src/cmd/cal.c

cal [ month ] [ year ]