Knowledge, negation, and incompatibility (1969), p. 583
by Englebretsen, George

Additional notes: Interpretation of the symbols (cf. pp. 581-582):

$S$ stands for 'a knows that p'
$\sim\!S$ stands for 'it is not the case that a knows that p'
$\overline{S}$ stands for 'a doesn't know that p'
$S-$ stands for 'a knows that -p'

Note that $\sim\!S$ has a different meaning than $\overline{S}$. After all, $\overline{S}$, i.e. 'a doesn't know that p', is equivalent to 'a merely believes or doubts or disbelieves or is uncertain about or ... p', and thus entails that a is at the very least aware of p, while $\sim\!S$, i.e. 'it is not the case that a knows that p' does NOT entail that a is even aware of p (cf. p. 582).