let L be with_suprema Poset; :: thesis: for X being Subset of L holds
( X c= downarrow (finsups X) & ( for I being Ideal of L st X c= I holds
downarrow (finsups X) c= I ) )
let X be Subset of L; :: thesis: ( X c= downarrow (finsups X) & ( for I being Ideal of L st X c= I holds
downarrow (finsups X) c= I ) )
A1: X c= finsups X by Th50;
finsups X c= downarrow (finsups X) by Th16;
hence X c= downarrow (finsups X) by A1, XBOOLE_1:1; :: thesis: for I being Ideal of L st X c= I holds
downarrow (finsups X) c= I
let I be Ideal of L; :: thesis: ( X c= I implies downarrow (finsups X) c= I )
assume A2: X c= I ; :: thesis: downarrow (finsups X) c= I
let x be set ; :: according to TARSKI:def 3 :: thesis: ( not x in downarrow (finsups X) or x in I )
assume A3: x in downarrow (finsups X) ; :: thesis: x in I
then reconsider x = x as Element of L ;
consider y being Element of L such that
A4: x <= y and
A5: y in finsups X by A3, Def15;
consider Y being finite Subset of X such that
A6: y = "\/" (Y,L) and
A7: ex_sup_of Y,L by A5;
consider i being Element of I;
reconsider i = i as Element of L ;
A8: ex_sup_of {i},L by YELLOW_0:38;
A9: sup {i} = i by YELLOW_0:39;

A10: now

assume ex_sup_of {} ,L ; :: thesis: "\/" ({},L) in I
then "\/" ({},L) <= sup {i} by A8, XBOOLE_1:2, YELLOW_0:34;
hence "\/" ({},L) in I by A9, Def19; :: thesis: verum

end;

Y c= I by A2, XBOOLE_1:1;
then y in I by A6, A7, A10, Th42;
hence x in I by A4, Def19; :: thesis: verum