anchor.diff:                  match implicitAlias (expr.Value, alias) with
                   | None -> Column (expr, None) |> Seq.singleton
                   | Some a -> Column (expr, Some (prefix + a)) |> Seq.singleton
  -                    
  -                        
  +                                     
       member this.ResultColumns(resultColumns : ResultColumns, knownShape : InferredQueryShape option) =
           let columns =
               resultColumns.Columns
  
positive.code:                     | Some withClause ->
                          let checker, withClause = this.WithClause(withClause)
                          checker, Some withClause
                  let compound = checker.Compound(select.Compound, None) // TODO possibly known shape from CTE
                  {   With = withClause
                      Compound = compound
                      OrderBy = Option.map (rmap checker.OrderingTerm) select.OrderBy
  
negative.code:                     Column = None
                  }
          }
  
      member this.Case(source : SourceInfo, case : CaseExpr) =
          let case =
              {   Input = Option.map this.Expr case.Input
  