`setmod'
--------

setmod([P])
     :: Sets the ground field to GF(P).

RETURN
     integer

N
     prime less than 2^27

   * Sets the ground field to GF(P) and returns the value P.

   * A member of a finite field does not have any information about the
     field and the arithmetic operations over GF(P) are applied with P
     set at the time.

   * As for large finite fields, *note Finite fields::.

     [0] A=dp_mod(dp_ptod(2*x,[x]),3,[]);
     (2)*<<1>>
     [1] A+A;
     addmi : invalid modulus
     return to toplevel
     [1] setmod(3);
     3
     [2] A+A;
     (1)*<<1>>

References
     *Note `dp_mod dp_rat': dp_mod dp_rat, *Note `Types of numbers':
     Types of numbers.

