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  usage: (ledit object)
h or ?  -- help
ok      -- end
q       -- quit (not saved)
p       -- level print
pp      -- pretty print
mark    -- stack cur_pointer
^ or top-- top level
<       -- pop cur_pointer
num     -- into the num-th element
- num   -- into the num-th element from the last
cdr     -- into cdr part
(bi n1 n2)        -- both in from n1 to n2 elements
(bo n)            -- both out from n-th element
(f s-exp)         -- find s-exp
(r s-exp s'-exp)  -- substitute all s-exp to s'-exp
(cdr n)           -- n-th cdr
(n s-exp)         -- append s-exp to the last
(num)             -- delete num-th element
(num { s-exp })   -- substitute num-th element to s-exp
(-num { s-exp })  -- insert s-exp into num-th element
(e { form1 .. formn })  -- eval from form1 to formn