1. Start by adding the XLO4+ filter code. XLO4+ eliminates xthStartOffOfLayoff >= 4.
2. Next add filter codes XLO1 and XLO2. These eliminate horses making xthStartOffOfLayoff = 1 and xthStartOffOfLayoff = 2 respectively.
3. Finally add the XLO0 filter code. XLO0 eliminates xthStartOffOfLayoff = 0 or horses that have never had a layoff.
When you are done, by process of elimination, what you are left with are horses making xthStartOffOfLayoff = 3. Your xthStartOffOfLayoff filter code line will look something like this: