anchor.diff:          Gen.oneof
               [
                   Gen.map3 (fun b expr1 expr2 -> SynExpr.Sequential(SequencePointsAtSeq, b, expr1, expr2, zero)) Arb.generate<_> genSubDeclExpr genSubSeqExpr
  -                Gen.map3 (fun b bindings expr -> SynExpr.LetOrUse(b, not b, bindings, expr, zero)) Arb.generate<_> generateSynBindingList genSubBasicExpr
  +                // Should not have 'use' keywords on the top level
  +                Gen.map3 (fun b bindings expr -> SynExpr.LetOrUse(b, false, bindings, expr, zero)) Arb.generate<_> generateSynBindingList genSubBasicExpr
               ]
   
   and generateDeclExpr size =
  
positive.code:         let genSubSynSimplePats = generateSynSimplePats (size/2)
          Gen.frequency 
              [ 
                  8, Gen.map3 (fun b bindings expr -> SynExpr.LetOrUse(b, not b, bindings, expr, zero)) Arb.generate<_> generateSynBindingList genSubDeclExpr //
                  4, Gen.map2 (fun expr clauses -> SynExpr.Match(NoSequencePointAtDoBinding, expr, clauses, false, zero)) genSubDeclExpr genSubSynMatchClauseList //                
                  2, Gen.map2 (fun b clauses -> SynExpr.MatchLambda(b, zero, clauses, NoSequencePointAtDoBinding, zero)) Arb.generate<_> genSubSynMatchClauseList //
                  2, Gen.map3 (fun b pat expr -> SynExpr.Lambda(b, false, pat, expr, zero)) Arb.generate<_> genSubSynSimplePats genSubDeclExpr //
                  1, Gen.map2 (fun expr1 expr2 -> SynExpr.TryFinally(expr1, expr2, zero, NoSequencePointAtTry, NoSequencePointAtFinally)) genSubDeclExpr genSubDeclExpr //
                  1, Gen.map2 (fun expr clauses -> SynExpr.TryWith(expr, zero, clauses, zero, zero, NoSequencePointAtTry, NoSequencePointAtWith)) genSubDeclExpr genSubSynMatchClauseList //
                  1, Gen.map (fun c -> SynExpr.Const(c, zero)) genSubSynConst //
  
negative.code:         |> Seq.toArray
      let startIndex = positions.[r.StartLine-1] + r.StartColumn
      let endIndex = positions.[r.EndLine-1] + r.EndColumn-1
      let sample = source.[startIndex..endIndex]
      // Avoid to recreate the same source
      // because it may cause the shrinker to loop forever
      if (sample.Trim()) = (originalSource.Trim()) then 
          None
      else Some (Input sample)
  
  let toSynExprs (Input s) =
      match (try Some (parse false s) with _ -> None) with
  