anchor.diff:  \   (doubleAlso) ( c-addr u -- x 1 | x x 2 )
   \               If the string is legal, give a single or double cell number
   \               and size of the number.
  -header negate   : negate    invert ;fallthru
   header 1+       : 1+        d# 1 + ;
  +header negate   : negate    invert 1+ ;
   header 1-       : 1-        d# -1 + ;
   header 0=       : 0=        d# 0 = ;
   header cell+    : cell+     d# 2 + ;
   
  -header 0<>      : 0<>       d# 0 ;fallthru
   header <>       : <>        = invert ; 
  +header 0<>      : 0<>       d# 0 <> ;
   header >        : >         swap < ; 
   header 0<       : 0<        d# 0 < ; 
   header 0>       : 0>        d# 0 > ;
  
positive.code: : jumptable ( u -- ) \ add u to the return address
      r> + >r ;
  
  : -throw ( a b -- ) \ if a is nonzero, throw -b
      negate and
  ;fallthru
  
  header throw
  : throw
      ?dup if
  
negative.code:     then
  ;
  
  : -throw ( a b -- ) \ if a is nonzero, throw -b
      negate and throw
  ;
  
  header abort
  : abort
      d# -1 throw
  