Operators for the "Date" class.
There is an Ops method and specific
methods for + and - for the Date class.
date + x
x + date
date - x
date1 lop date2date objects
date objects or character vectors. (Character
vectors are converted by as.Date.)
a numeric vector (in days) or an object of class
"difftime", rounded to the nearest whole day.
One of ==, !=, <, <=, >
or >=.
x does not need to be integer if specified as a numeric vector,
but see the comments about fractional days in the help for
Dates.