boost::logic::operator!= — Compare tribools for inequality.
tribool operator!=(tribool x, tribool y); tribool operator!=(tribool x, bool y); tribool operator!=(bool x, tribool y); tribool operator!=(indeterminate_keyword_t, tribool x); tribool operator!=(tribool x, indeterminate_keyword_t);
the result of comparing two tribool values for inequality, according to the following table:
!=