
theorem Th4:
  for n being Nat st n in 4k+3_Primes holds n >= 3
  proof
    let n be Nat;
    assume n in 4k+3_Primes;
    then consider k being Nat such that
    A1: n=4*k+3 & n is prime by Def1;
    thus n >= 3 by A1,NAT_1:11;
  end;
