gistfile1.txt

when the entry label to a function is originally declared (during macro expansion),
the entry label is tagged with the label that was active when the label was declared;
this is called the scope label.

later, during evaluation, when an entry label is encountered as argument, and the 
label has a scope label tag, the current frame (a cactus stack) is searched upwards
for the scope label, and truncated by that amount.

if the scope label tag can not be found in upwards frames (and this is the part that 
gives me grief, because it happens too much) then the current frame is taken as-is.

the closure is then formed from the entry label and the frame.

so, in short: closure is formed from the active frame + label by default, but if we
can truncate the frame, we do.