Hi Balaji,
Assuming `.` is of type xs:date, then you should be able to use the following to check that the date is the first of the month:
day-from-date(.) = 1
E.g.:
day-from-date(xs:date('2017-04-05')) = 1 ⇒ returns false
day-from-date(xs:date('2017-04-01')) = 1 ⇒ returns true
You'll let us know if this works for you,
Alex
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