[stack] S-K Construction of Dip?

From http://tunes.org/~iepos/joy.html

This sentence never quite sat well with me:

"however, there is no way to form "dip" or "sip" using just "s" and
"k" because, roughly speaking, they provide no way to dequote items
buried in the stack."

I may have found a counter-example:

We know that we can construct: c b and i from s

Then we can go on to define:

swap = [] c
cons = [] b
zap = [] k
unit = [] [zap] s
cat = swap [i] cons swap cons

And finally:

dip = swap unit cat i

Can anyone verify if this is this correct for me?

Thanks,
Chrstopher