In his article on Virtual Environments (a part of his VFSM specification method) Ferdinand Wagner describes some new ways of thinking about Boolean Algebra as a software design tool.  On page 4 of this PDF article, when describing operators in his system he says this:Control statements need Boolean  values. Hence, the names must be used  to produce Boolean results. To achieve  this we want to combine them together  using Boolean operators. There is  nothing wrong with usage of AND and OR  operators with their Boolean meaning.  For instance, we may write:DI_ON OR AI_LARGER_THAN_8.1 AND  TIMER_OVERto express the control situation:  digital input is on or analog input is  larger than 8.1 and timer is over.We cannot use the NOT operator,  because the result of the Boolean  negation makes sense only for true  Boolean values. The result of, for  instance, NOT (AI_LARGER_THAN_8.1)would be ambiguous.If AI_LARGER_THAN_8.1 is acceptable, why would he consider NOT (AI_LARGER_THAN_8.1) to be ambiguous?
Why does F. Wagner consider NOT (AI_LARGER_THAN_8.1) to be ambiguous?
design;finite state machine
There's an error in this paper.  Wagner claims this is boolean algebra, but also includes 'UNKNOWN' as a value along with TRUE and FALSE.  Therefore, this is not actually boolean algebra but a trinary system of his own creation.Notably, he does not define NOT with respect to this trinary system.  This is a classic gotcha in trinary systems.  Unlike a binary system, NOT TRUE does not necessarily equal FALSE, nor does NOT FALSE necessarily equal TRUE.