let L be sup-Semilattice; :: thesis: for x being Element of L holds
( x is co-prime iff for A being non empty finite Subset of L st x <= sup A holds
ex a being Element of L st
( a in A & x <= a ) )

let x be Element of L; :: thesis: ( x is co-prime iff for A being non empty finite Subset of L st x <= sup A holds
ex a being Element of L st
( a in A & x <= a ) )

thus ( x is co-prime implies for A being non empty finite Subset of L st x <= sup A holds
ex a being Element of L st
( a in A & x <= a ) ) :: thesis: ( ( for A being non empty finite Subset of L st x <= sup A holds
ex a being Element of L st
( a in A & x <= a ) ) implies x is co-prime )
proof
assume x is co-prime ; :: thesis: for A being non empty finite Subset of L st x <= sup A holds
ex a being Element of L st
( a in A & x <= a )

then A1: x ~ is prime ;
let A be non empty finite Subset of L; :: thesis: ( x <= sup A implies ex a being Element of L st
( a in A & x <= a ) )

reconsider A1 = A as non empty finite Subset of (L ~) ;
assume x <= sup A ; :: thesis: ex a being Element of L st
( a in A & x <= a )

then A2: x ~ >= (sup A) ~ by LATTICE3:9;
A3: ex_sup_of A,L by YELLOW_0:54;
then "\/" (A,L) is_>=_than A by YELLOW_0:def 9;
then A4: ("\/" (A,L)) ~ is_<=_than A by YELLOW_7:8;
A5: now :: thesis: for y being Element of (L ~) st y is_<=_than A holds
y <= ("\/" (A,L)) ~
let y be Element of (L ~); :: thesis: ( y is_<=_than A implies y <= ("\/" (A,L)) ~ )
assume y is_<=_than A ; :: thesis: y <= ("\/" (A,L)) ~
then ~ y is_>=_than A by YELLOW_7:9;
then ~ y >= "\/" (A,L) by ;
hence y <= ("\/" (A,L)) ~ by YELLOW_7:2; :: thesis: verum
end;
ex_inf_of A,L ~ by ;
then (sup A) ~ = inf A1 by ;
then consider a being Element of (L ~) such that
A6: ( a in A1 & x ~ >= a ) by A1, A2, Th22;
take ~ a ; :: thesis: ( ~ a in A & x <= ~ a )
thus ( ~ a in A & x <= ~ a ) by ; :: thesis: verum
end;
thus ( ( for A being non empty finite Subset of L st x <= sup A holds
ex a being Element of L st
( a in A & x <= a ) ) implies x is co-prime ) :: thesis: verum
proof
assume A7: for A being non empty finite Subset of L st x <= sup A holds
ex a being Element of L st
( a in A & x <= a ) ; :: thesis: x is co-prime
now :: thesis: for a, b being Element of (L ~) holds
( not a "/\" b <= x ~ or a <= x ~ or b <= x ~ )
let a, b be Element of (L ~); :: thesis: ( not a "/\" b <= x ~ or a <= x ~ or b <= x ~ )
set A = {(~ a),(~ b)};
assume a "/\" b <= x ~ ; :: thesis: ( a <= x ~ or b <= x ~ )
then x <= ~ (a "/\" b) by YELLOW_7:2;
then ( sup {(~ a),(~ b)} = (~ a) "\/" (~ b) & x <= (~ a) "\/" (~ b) ) by ;
then consider l being Element of L such that
A8: l in {(~ a),(~ b)} and
A9: x <= l by A7;
( l = ~ a or l = ~ b ) by ;
hence ( a <= x ~ or b <= x ~ ) by ; :: thesis: verum
end;
then x ~ is prime ;
hence x is co-prime ; :: thesis: verum
end;