now :: thesis: ( not 2 divides 347 & not 3 divides 347 & not 5 divides 347 & not 7 divides 347 & not 11 divides 347 & not 13 divides 347 & not 17 divides 347 )

347 = (2 * 173) + 1 ;
hence not 2 divides 347 by NAT_4:9; :: thesis: ( not 3 divides 347 & not 5 divides 347 & not 7 divides 347 & not 11 divides 347 & not 13 divides 347 & not 17 divides 347 )
347 = (3 * 115) + 2 ;
hence not 3 divides 347 by NAT_4:9; :: thesis: ( not 5 divides 347 & not 7 divides 347 & not 11 divides 347 & not 13 divides 347 & not 17 divides 347 )
347 = (5 * 69) + 2 ;
hence not 5 divides 347 by NAT_4:9; :: thesis: ( not 7 divides 347 & not 11 divides 347 & not 13 divides 347 & not 17 divides 347 )
347 = (7 * 49) + 4 ;
hence not 7 divides 347 by NAT_4:9; :: thesis: ( not 11 divides 347 & not 13 divides 347 & not 17 divides 347 )
347 = (11 * 31) + 6 ;
hence not 11 divides 347 by NAT_4:9; :: thesis: ( not 13 divides 347 & not 17 divides 347 )
347 = (13 * 26) + 9 ;
hence not 13 divides 347 by NAT_4:9; :: thesis: not 17 divides 347
347 = (17 * 20) + 7 ;
hence not 17 divides 347 by NAT_4:9; :: thesis: verum

end;

then for n being Element of NAT st 1 < n & n * n <= 347 & n is prime holds
not n divides 347 by XPRIMET1:14;
hence 347 is prime by NAT_4:14; :: thesis: verum