UNTELL-INSTANCE-VALUE ===================== syntax: (untell-instance-value <evaluates-to relation-name> <evaluates-to instance-spec> <lisp-type: T> [:write-dependents {T | NIL | Var}] [:probe {T | NIL | :and-do | Var}]) This function removes an element from the value set of the instance relation. If ':write-dependents' is not set to NIL, then the write-dependents will be informed after the value set is changed. The changed value set or NIL, when the element is not included in the value set, will be returned as value. example: >(untell-instance-value 'offer Paris Louvre) #<set-of OFFER (...)> >(untell-instance-value 'offer Paris Big-Ben) NIL