anchor.diff:      let meltHBNeighbour = 60.0<C>
       let maxOligoLen = dp.pp.maxLength
   
  -    let upRev = revComp up
  +    let upRev = up.RevComp()
       // TODO - if we are near the 5' end of the gene we should use non rare
       // codons.  Can't currently figure out position from params
       // Also need to ensure we don't chew back past 5' start codon
  
positive.code:         (down.Length/3*3)
          |> min (match targetAALen with | None -> 120 | Some(v) -> v*3)
  
      let downTrans = down.[0..transLen-1] |> (if fwd then id else revComp)
      let current = downTrans |> translate
  
      // Pick alternative codons
      let alt =
  
negative.code:         (minFreq:float)
          (targetAALen : int option)
          (pp: DesignParams)
          (up: Dna)
          (prefix: Dna)
          (down: Dna) =
      generateHBCore cl minFreq targetAALen pp true up prefix down    
  
  /// Create a heterology block, removing part of the left hand (up) slice sequence and replacing with a rewritten sequence    
  