theorem
  card {x1,x2,x3,x4,x5,x6,x7,x8} <= 8
proof
  card {x2,x3,x4,x5,x6,x7,x8} <= 7 by Th54;
  then
A1: 1 + card {x2,x3,x4,x5,x6,x7,x8} <= 1+7 by XREAL_1:7;
  {x1,x2,x3,x4,x5,x6,x7,x8} = {x1} \/ {x2,x3,x4,x5,x6,x7,x8} & card {x1} =
  1 by CARD_1:30,ENUMSET1:22;
  then card {x1,x2,x3,x4,x5,x6,x7,x8} <= 1 + card {x2,x3,x4,x5,x6,x7,x8} by
Th42;
  hence thesis by A1,XXREAL_0:2;
end;
