type of dictionary int to int inside other type

"Ilia Rassadzin [email protected] [ocaml_beginners]" <[email protected]>
Newsgroups gmane.comp.lang.ocaml.beginners
Message-ID <[email protected]>
Hello,
I have a beginner question:
I am trying to declare a type 
type point =
    { id                    : int;
      x                     : int;
      y                     : int;
      z                     : int;
      pref                  :  <type definition goes here>;
      mutable obj_id     : int;
      modulo_squared        : int;      
      cos_phi               : float;
      cos_theta             : float;
      mutable cos_circle    : float;
      mutable eff_modulo    : float;
};; 

pref is a pythonic dictionary int to int.
how to implement it?
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