SETDIF: Perform a set difference operation on two positive integer sets
SETDIF(A,B,C), will assign to set A: B - C

syntax: SETDIF(target_letter, set_letter1, set_letter2)

Performs a set difference operation on the sets with the letter variable <set_letter1> and <set_letter2> which refers to letter variable ($A...$Z) then puts the results from the set difference operation into <target_letter> set.