This might be a very easy question but I just wanted to make myself clear on it.
This is to be done in a validation rule formula. Say the date time field is Test__c
1) I need to compare a date time field value if it is greater than Yesterday.
2) Compare a date time field value if greater than a specific date.
3) greater than LAST_N_DAYS: 2 (What this actually mean? Day before yesterday or a day even before that?)