anchor.diff:  : 1-  1 - ;
   : INVERT  TRUE XOR ;
   : NEGATE  INVERT 1+ ;
  +: DNEGATE  INVERT SWAP NEGATE SWAP OVER 0= - ;      \ word set DOUBLE
   : *  UM* DROP ;
   : S>D  DUP 0< ;
   : ABS  S>D IF NEGATE THEN ;
  +: DABS  DUP 0< IF DNEGATE THEN ;                    \ word set DOUBLE
   
   : +!  \  ( n a-addr -- )
       DUP @ ROT + SWAP ! ;
  
positive.code: : .  ( n -- )
      DUP ABS 0 <# #S ROT SIGN #> TYPE SPACE ;
  
  
  @@
  : ?PAIRS  - IF ABORT" unmatched conditionals" THEN ;
  
negative.code: \ block for WORD.
  \ This word is part of core ext, but it is very nice for parsing
  \ and used here anyway.
  : PARSE  \ ( char "ccc<char>" -- c-addr u )                     \ word set CORE EXT
      PARSE-POS 0 ROT SWAP
      SRC-SPAN IF
        DO
  