anchor.diff:  
       member __.Resolve(force, getSha1, getVersionF, getPackageDetailsF, groupsToResolve:Map<GroupName,RequirementsGroup>) =
           groupsToResolve
  -        |> Map.map (fun k group ->  
  +        |> Map.map (fun k group ->
               let rootDependencies =
                   match group.RootDependencies with
                   | None -> groups.[k].Packages
  
positive.code:             else
                  rest,""
  
          if operators |> Seq.exists (fun x -> prereleases.Contains x) || prereleases.Contains("!") then
              failwithf "Invalid prerelease version %s" prereleases
  
          { Sources = sources
  
negative.code:               Sources = []
                Packages = []
                RemoteFiles = [] }
  
          member this.CombineWith (other:DependenciesGroup) =
              { Name = this.Name
                Options = 
                  { Redirects = this.Options.Redirects || other.Options.Redirects
                    Settings = this.Options.Settings + other.Options.Settings
                    Strict = this.Options.Strict || other.Options.Strict }
                Sources = this.Sources @ other.Sources |> List.distinct
                Packages = this.Packages @ other.Packages
                RemoteFiles = this.RemoteFiles @ other.RemoteFiles }
  
  type RequirementsGroup = {
      Name: GroupName
  