
theorem Th12: :: Even102
  for n being even Nat st n<=5 holds n=0 or n=2 or n=4
proof
  let n be even Nat such that
A1: n<=5;
  n<>2*2+1;
  then n<4+1 by A1,XXREAL_0:1;
  then
A2: n<=4 by NAT_1:13;
  per cases by A2,XXREAL_0:1;
  suppose
    n=4;
    hence thesis;
  end;
  suppose
    n<3+1;
    then n<=3 by NAT_1:13;
    hence thesis by Th11;
  end;
end;
