In set and logic I interpret this as "(not the set {p v q}) less r". I assume that "not the set {p v q}" means the rest of the alphabet {a b c d e f g h I j k l m n o r s t u w x y z} and "less r" means remove r from the set so we have:
{a b c d e f g h I j k l m n o s t u w x y z}
The order is not important and we can usually mix the letters up if we want to.