Solution to 9.

9. It's not true that neither Gertrude nor I can knit.

Doing the grouping first, we see:

It's not true that (neither Gertrude nor I can knit).

If we expand the compound subject, we get

It's not true that (neither Gertrude can knit nor I can knit).

The simple statements are

G = Gertrude can knit.

I = I can knit.

And substituting we get:

It's not true that (neither G nor I)

Doing the 'neither ... nor ...' as a negated disjunction, we get

It's not true that {not-(G or I)}

Which is simply:

not-{not-(G or I)}

Which is