PROCEDURE FirstPosition(READONLY x : T) : CARDINAL;
  (* 
    Returns the initial position where is the number "x" excluding its signal *)

PROCEDURE GetSign(READONLY x : T) : Sign;
  (* 
    Returns the sign of the number "x", that is, 
            -1 if x < 0;  
             0 if x = 0;
            +1 if x > 0. *)

PROCEDURE IsZero(READONLY x : T) : BOOLEAN;
  (* 
    Returns TRUE iff x=0.                        *)

PROCEDURE NumDigits(READONLY x : T) : SizeT;
  (* 
    Returns the number of the digits used by x, not considering leading
    zeros. If x=0 then returns 1.  *)

PROCEDURE Sub(VAR z: T; READONLY x,y : T);
  (* 
    Computes "z=x - y"; Requires |x| >= |y| *)

PROCEDURE Div(VAR z : T; READONLY x,y : T; ); 
  (* 
    Computes "z = x DIV y", where DIV is the integer numbers division.  
               if y=0 then returns NIL;
               if y>0 then returns FLOOR(x/y) 
               if y<0 then returns CEIL(x/y).  *)

PROCEDURE Mod(VAR z : T; READONLY x,y : T; ); 
  (* 
    Computes "z = x MOD y" *)

PROCEDURE FromInteger(VAR z: T; i : INTEGER);
  (* 
    Writes on "z" the number whose value is given by the integer
    number i.  *)

PROCEDURE ToInteger(READONLY x : T) : INTEGER;
  (* 
    Returns the integer number corresponding to the value of the first
    digit in the number "x".  Note: This is the unique integer congruent
    to z mod 2^(31) *)