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These functions perform calendrical computations using time values (see Time of Day).

- Function:
**time-less-p***t1 t2* This returns

`t`

if time value`t1`is less than time value`t2`.

- Function:
**time-subtract***t1 t2* This returns the time difference

`t1`-`t2`between two time values, as a time value.

- Function:
**time-add***t1 t2* This returns the sum of two time values, as a time value. One argument should represent a time difference rather than a point in time. Here is how to add a number of seconds to a time value:

(time-add

`time``seconds`)

- Function:
**time-to-days***time-value* This function returns the number of days between the beginning of year 1 and

`time-value`.

- Function:
**time-to-day-in-year***time-value* This returns the day number within the year corresponding to

`time-value`.

- Function:
**date-leap-year-p***year* This function returns

`t`

if`year`is a leap year.