anchor.diff:  
   [<Test>]
   let ``exact cover problems with no solutions``() =
  -    let body = fun matrix ->
  +    let body matrix =
           let dlx = new Dlx()
           let solutions = dlx.Solve matrix |> Seq.toList
           solutions.Length = 0 |@ sprintf "Expected no solutions but got %d" solutions.Length
  
positive.code: let genPartitionedSolution numCols startIdx endIdx =
      gen {
          let! numSolutionRows = choose (1, min 5 (endIdx - startIdx))
          let! solutionRows = genPartitionedSolutionRows numCols startIdx endIdx numSolutionRows
          return solutionRows
      }
  
  let genPartitionedSolutions numCols partitions =
  
negative.code:         let! prefixPart = listOfLength prefixPartLength (constant fillerValue)
          let! randomPart = listOfLength randomPartLength (constant 0)
          let! suffixPart = listOfLength suffixPartLength (constant fillerValue)
          return List.concat [prefixPart; randomPart; suffixPart]
      }
  
  let randomlySprinkleOnesIntoSolutionRows solutionRows startIdx randomRowIdxs =
  