anchor.diff:  let constFold0Index_exp = 
     <@ 
       %i + 0
  +    <==>
  +    %i
  +  @>
  +
  +let constFoldN0Index_exp = 
  +  <@ 
  +    %i - 0
       <==>
       %i
     @>
  
positive.code:     (%FIN) %i
    @>
  
  let comAddIndex_exp = 
    <@
      %i + %j
  
negative.code:     %i + (%j - %k)
    @>
  
  let assocSubAddIndex_exp = 
    <@
      (%i - %j) + %k
      <==>
      %i - (%j - %k)
    @>
  
  let assocSubSubIndex_exp = 
    <@
      (%i - %j) - %k
      <==>
      %i - (%j + %k)
    @>
  
  let subSameIndex_exp = 
    <@
      %i - %i
  