KeyValuePair is not defined when invoking a method that requires that type as an argument <p>I receive the following error when attempting to invoke the function, "columnHasStreak" using REPL:</p> <blockquote> <p>error FS0039: The type 'KeyValuePair' is not defined</p> </blockquote> <p>I am attempting to run the following code using REPL:</p> <p>module TicTacToe</p> <pre><code>open FsUnit open NUnit.Framework open System.Collections.Generic [&lt;Test&gt;] let ``some test to help me learn F#`` () = let columnHasStreak (column : list&lt;KeyValuePair&lt;int,bool&gt;&gt;) = column |&gt; Seq.forall (fun cell -&gt; cell.Value) let cells = [0..8] let connectCount = 3; let columns = [0..2]; let grid = [for cell in cells -&gt; (cell, true)] |&gt; Map.ofSeq let rowLocations = grid |&gt; Seq.chunkBySize connectCount |&gt; Seq.toList let columnLocations = [for i in columns -&gt; rowLocations|&gt; List.map (fun row -&gt; row.[i])] let allColumnsHaveStreak = [for i in columns -&gt; columnLocations.[i]] |&gt; Seq.forall (fun column -&gt; column |&gt; columnHasStreak) </code></pre> <p>Can someone explain to me why I am receiving this error?</p>