anchor.diff:                  // add entry with recursion
                   let idx = hashToIndex hkv.H dep
                   let entry = arr.[idx]
  -                let arr = arr.Clone () :?> Vnode<'k, 'v> array
  -                arr.[idx] <- add5 hkv (dep + 1) mdep entry
  +                let arr = cloneArray arr
  +                arr.[idx] <- add hkv earr mdep (dep + 1) entry
                   Multiple arr
   
               | Clash _ ->
  
positive.code:     let makeEmpty mdep =
          if mdep > 6 then failwith "Vmap max depth should not be greater than 6."
          elif mdep < 0 then failwith "Vmap max depth should not be less than 0."
          else { Mdep = mdep; Vnode = Vnode.empty }
  
      let add k v map =
          { map with Vnode = Vnode.add k v map.Mdep map.Vnode }
negative.code:                 let idx = hashToIndex hkv.H dep
                  let idx' = hashToIndex hkv'.H dep
                  if idx <> idx' then
                      let arr = cloneArray earr
                      arr.[idx] <- Singlet hkv
                      arr.[idx'] <- Singlet hkv'
                      Multiple arr
  