
theorem Th13: :: Even103
  for n being even Nat st n<=7 holds n=0 or n=2 or n=4 or n=6
proof
  let n be even Nat such that
A1: n<=7;
  n<>2*3+1;
  then n<6+1 by A1,XXREAL_0:1;
  then
A2: n<=6 by NAT_1:13;
  per cases by A2,XXREAL_0:1;
  suppose
    n=6;
    hence thesis;
  end;
  suppose
    n<5+1;
    then n<=5 by NAT_1:13;
    hence thesis by Th12;
  end;
end;
