This is the "plai-typed" package, which provides the "plai-typed"
collection for Racket v5.3.2 or later.

It's meant to be installed with the Racket package manager:

 * In recent versions of DrRacket, choose "Install Package.."
   from the "File" menu, and enter

       plai-typed

   in the dialog.

 * From the comamnd line:

     raco pkg install plai-typed