anchor.diff:  
   open FSharp.Compatibility.OCaml
   open FSharp.Compatibility.OCaml.Num
  +
  +open ExtCore.Control
   
   open NHol
   open lib
  
positive.code: (* ------------------------------------------------------------------------- *)
  (* More stuff about equality.                                                *)
  (* ------------------------------------------------------------------------- *)
  let EQ_REFL = 
      prove((parse_term @"!x:A. x = x"), 
            GEN_TAC
  
negative.code:                 toks
          pa_intro
      let DESTRUCT_TAC s = 
          let tac, rest = (fix "Destruct pattern" parse_destruct << lex << explode) s
          if rest = []
          then tac
          else fun _ _ -> Choice.failwith "Garbage after destruct pattern"
      let INTRO_TAC s = 
          let tac, rest = (fix "Introduction pattern" parse_intro << lex << explode) s
          if rest = []
          then tac
          else fun _ -> Choice.failwith "Garbage after intro pattern"
      let FIX_TAC s = 
          let tac, rest = (parse_fix << lex << explode) s
          if rest = []
          then tac
          else fun _ -> Choice.failwith "FIX_TAC: invalid pattern"
      DESTRUCT_TAC, FIX_TAC, INTRO_TAC
  