procedure ldag(stree,done)
   local a
   /done := table()		# start table
				# return list if done
   if a := \done[stree] then return a
   stree ?			# build like a tree
      if a := [tab(upto('('))] then {
         move(1)
         while put(a,ldag(tab(bal(',)')),done)) do
            move(1)
         }
      else a := [tab(0)]
   return done[stree] := a	# put in table
end
