anchor.diff:  header-imm do
   :noname
       do-common
  +: dotail
       tbegin
       inline: >r
   ;
  
positive.code:         dup
      while
          dup @ swap        ( next leafptr )
          dp @i 2/ swap _!
      repeat
      drop
      leaves _!
  
negative.code: ;
  
  : (loopnext)
      d# 1 + d# 0 over=
  ;
  
  header-imm loop
  