In addition to boolean T-F, they have an "undetermined" or "null" value N The truth table in the book for this logic goes like this: "OR" T v N = T F v N = N "AND" T ^ N = N F ^ N = F it does not make sence unless I assume N to be unknown in a sense of unknown whether N = T or F, i.e. N = (T v F). If N is considered to be a null it does not make sense at all! Is my assumption correct? or if not, could someone shed clarity on this Thanks.