"Date" class. There is an Ops method and specific
methods for + and - for the Date class.date + x
x + date
date - x
date1 lop date2as.Date.)"difftime", rounded to the nearest whole day.==, !=, <, <=, >
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.