[(q)uibble: main entry point. print brackets, calling n in between if stack not
 empty.]sx
[ [{]n z 0 !=n [}]pR ]sq

[(n)onempty: if more than 1 item, call m. then print top of stack.]sx
[ z 1 !=m n ]sn

[(m)ore: call f to flip stack into r register, call p to print most of it,
 then pop the last item back onto the main stack so it's there to be printed
 after we return]sx
[ lfx lpx Lr ]sm

[(f)lip: utility routine to reverse the stack into the r register]sx
[ Sr z 0 !=f ]sf

[(p)rint: get next item from stack in r register and print it. If there are
 more than 2 items left on the register stack (which never drops below one
 item), print a comma (c) and recurse. If there are exactly two items left,
 print " and " (a) and return.]sx
[ Lr n 2 yr >c 2 yr =a 2 yr >p]sp

[(c)omma: utility routine to print a comma followed by a space]sx
[ [, ]n ]sc

[(a)and: utility routine to  print " and "]sx
[ [ and ]n ]sa

[run tests]sx
lqx
[ABC] lqx
[ABC] [DEF] lqx
[ABC] [DEF] [G] [H] lqx