This is a simple way to determine if a year is a leap year or not using Lotus Notes @Formula in one @if statement.
The 3 rules are:
True if it is divisible by 4
False if it is divisible by 100
TRUE if it is divisble by 400
@if(@Modulo(@Year(@Today);4) =0 & @Modulo(@Year((@Today);100) <> 0
|@Modulo(@Year((@Today);400)=0;"Is Leap Year";"Is not Leap Year")