Just being out of the box - perhaps the "-" is the "wart"?
frame: context of 'n
and
head: head of s
I admit that the "of" looks superfluous in the second example compared with prior experience, but not if one wants "head" as a variable.
It is also meant to point to the dual meanings of the word "head", each meaning valid for different contextual notions. Mixing the same symbols from different contextual notions in the same expression is not something that has been cracked in Rebol yet, imo. I'm still hanging out for the "relative expression" promise to be fulfilled 