let x1, x2, x3, x4, x5, x6 be object ; :: thesis: card {x1,x2,x3,x4,x5,x6} <= 6
card {x2,x3,x4,x5,x6} <= 5 by Th52;
then A1: 1 + (card {x2,x3,x4,x5,x6}) <= 1 + 5 by XREAL_1:7;
( card {x1} = 1 & {x1,x2,x3,x4,x5,x6} = {x1} \/ {x2,x3,x4,x5,x6} ) by CARD_1:30, ENUMSET1:11;
then card {x1,x2,x3,x4,x5,x6} <= 1 + (card {x2,x3,x4,x5,x6}) by Th42;
hence card {x1,x2,x3,x4,x5,x6} <= 6 by A1, XXREAL_0:2; :: thesis: verum