anchor.diff:  
       let (|StartsWith|_|) pattern (str: string) =
           if str.StartsWith pattern then Some pattern else None
  +        
  +    let (|ContainsKey|_|) key (dic: System.Collections.Generic.IDictionary<'k,'v>) =
  +        let success, value = dic.TryGetValue key
  +        if success then Some value else None
   
       let ident name =
           Fabel.IdentValue {name=name; typ=Fabel.UnknownType} |> Fabel.Value
  
positive.code:         | "ofSeq" -> failwith "TODO"
          | "partitition" -> failwith "TODO"
          | "pick" -> failwith "TODO"
          | "remove" -> failwith "TODO"
          | "toArray" -> failwith "TODO"
          | "toList" -> failwith "TODO"
          | "toSeq" -> failwith "TODO"
          | "tryFindKey" -> failwith "TODO"
          | "tryPick" -> failwith "TODO"
          | _ -> NoMapping
          |> mapMethod com info
  // TODO: Static methods
  // let add k v (m:Map<_,_>) = m.Add(k,v)
  // let containsKey k (m:Map<_,_>) = m.ContainsKey(k)
  
negative.code: module Fabel.Plugins.Replacements
  open Fabel
  open Fabel.AST
  
  module private Util =
      let [<Literal>] system = "System."
  