With the exception of AND, OR, and NOT, all Verity operators require that you use angle brackets around them. This tells Verity that you're interested in actually using the NEAR operator, for example, rather than just trying to search for the word near in your document. The following line is not searching for the word near, but making use of NEAR:
CRITERIA="Sick <NEAR> Days"
AND, OR, and NOT, on the other hand, do not need the angle bracketsthey get used very often, and people only infrequently need to search for the actual words and, or, or not in their documents. The following two lines are equivalent:
CRITERIA="Sick AND Days" CRITERIA="Sick <AND> Days"