let X be set ; :: thesis: for x1, x2, x3, x4, x5 being Element of X st X <> {} holds
{x1,x2,x3,x4,x5} is Subset of X
let x1, x2, x3, x4, x5 be Element of X; :: thesis: ( X <> {} implies {x1,x2,x3,x4,x5} is Subset of X )
assume A1:
X <> {}
; :: thesis: {x1,x2,x3,x4,x5} is Subset of X
{x1,x2,x3,x4,x5} c= X
proof
let x be
set ;
:: according to TARSKI:def 3 :: thesis: ( not x in {x1,x2,x3,x4,x5} or x in X )
assume A2:
x in {x1,x2,x3,x4,x5}
;
:: thesis: x in X
( not
x in {x1,x2,x3,x4,x5} or
x = x1 or
x = x2 or
x = x3 or
x = x4 or
x = x5 )
by ENUMSET1:def 3;
hence
x in X
by A1, A2, Def2;
:: thesis: verum
end;
then
{x1,x2,x3,x4,x5} in bool X
by ZFMISC_1:def 1;
hence
{x1,x2,x3,x4,x5} is Subset of X
by Def2; :: thesis: verum