错误FS0193:类型约束不匹配

获取错误:

error FS0193: Type constraint mismatch. The type 
    'Map<ContentAndYear,DemoMap>'    
is not compatible with type
    'seq<ContentAndYear * DemoMap>

有问题的代码: Demo 是发生错误的地方。

type Demo = Map<ContentAndYear,DemoMap>

type ContentAndYear = Content * Year

let demoMap =
    dataMap
    |> Seq.ofList
    |> Seq.map(fun (content, data) ->
        { Content = content
          Year = data.Year
          Person = data.Person
          NullContent = nullContent.[content].contentraw
          PercentContent = nullContent.[content].contentraw
        })
    |> List.ofSeq

let demolist = 
    demoMap
    |> List.map (fun x -> (x.Content,x.Year) |> ContentAndYear,x)
    |> Map.ofList 

let x = demolist |> Demo  <---- Problem Line

如何解决?不确定。