Recall that an interpretation I in SL assigns each atomic wff $T$ or F but not both and assigns an $n-$ary truth function to each $n-$place operator with our operators receiving their standard interpretations. Suppose we want to prove by induction that an interpretation will assign any wff from our language $($atomic or molecular$)$ either T or F but not both. The base case would be atomics, which, by the definition of an interpretation, are trivially either $T$ or F but not both.

Now suppose we're considering an arbitrary wff $$ of the form not$.$ What do we assume about $$ in this case?

That it has the value $T$

That it has the value T or F but not both

That it is an atomic wff

That it has both of the values $T$ and $F$