let O1 be Ordinal; :: thesis: for L being complete Lattice
for f being monotone UnOp of L
for a being Element of L st a [= f . a & f,O1 +. a is_a_fixpoint_of f holds
for O2 being Ordinal st O1 c= O2 holds
f,O1 +. a = f,O2 +. a
let L be complete Lattice; :: thesis: for f being monotone UnOp of L
for a being Element of L st a [= f . a & f,O1 +. a is_a_fixpoint_of f holds
for O2 being Ordinal st O1 c= O2 holds
f,O1 +. a = f,O2 +. a
let f be monotone UnOp of L; :: thesis: for a being Element of L st a [= f . a & f,O1 +. a is_a_fixpoint_of f holds
for O2 being Ordinal st O1 c= O2 holds
f,O1 +. a = f,O2 +. a
let a be Element of L; :: thesis: ( a [= f . a & f,O1 +. a is_a_fixpoint_of f implies for O2 being Ordinal st O1 c= O2 holds
f,O1 +. a = f,O2 +. a )
assume A1: ( a [= f . a & f,O1 +. a is_a_fixpoint_of f ) ; :: thesis: for O2 being Ordinal st O1 c= O2 holds
f,O1 +. a = f,O2 +. a
set fa = f,O1 +. a;
defpred S₁[ Ordinal] means ( O1 c= $1 implies f,O1 +. a = f,$1 +. a );
A2: S₁[ {} ] ;

A3: now

let O2 be Ordinal; :: thesis: ( S₁[O2] implies S₁[ succ O2] )
assume A4: S₁[O2] ; :: thesis: S₁[ succ O2]
thus S₁[ succ O2] :: thesis: verum

proof

assume A5: O1 c= succ O2 ; :: thesis: f,O1 +. a = f,(succ O2) +. a

per cases ( O1 = succ O2 or O1 <> succ O2 ) ;

suppose O1 = succ O2 ; :: thesis: f,O1 +. a = f,(succ O2) +. a

hence f,O1 +. a = f,(succ O2) +. a ; :: thesis: verum

end;

suppose O1 <> succ O2 ; :: thesis: f,O1 +. a = f,(succ O2) +. a

then O1 c< succ O2 by A5, XBOOLE_0:def 8;
then O1 in succ O2 by ORDINAL1:21;
hence f,O1 +. a = f . (f,O2 +. a) by A1, A4, ABIAN:def 3, ORDINAL1:34
.= f,(succ O2) +. a by Th18 ;
:: thesis: verum

end;

end;

end;

end;

A6: now

let O2 be Ordinal; :: thesis: ( O2 <> {} & O2 is limit_ordinal & ( for O3 being Ordinal st O3 in O2 holds
S₁[O3] ) implies S₁[O2] )
assume A7: ( O2 <> {} & O2 is limit_ordinal & ( for O3 being Ordinal st O3 in O2 holds
S₁[O3] ) ) ; :: thesis: S₁[O2]
thus S₁[O2] :: thesis: verum

proof

deffunc H₁( Ordinal) -> Element of L = f,$1 +. a;
consider L1 being T-Sequence such that
A8: ( dom L1 = O2 & ( for O3 being Ordinal st O3 in O2 holds
L1 . O3 = H₁(O3) ) ) from ORDINAL2:sch 2();
A9: f,O2 +. a = "\/" (rng L1),L by A7, A8, Th20;
rng L1 is_less_than f,O1 +. a

proof

let q be Element of L; :: according to LATTICE3:def 17 :: thesis: ( not q in rng L1 or q [= f,O1 +. a )
assume q in rng L1 ; :: thesis: q [= f,O1 +. a
then consider O3 being set such that
A10: ( O3 in dom L1 & q = L1 . O3 ) by FUNCT_1:def 5;
reconsider O3 = O3 as Ordinal by A10;

per cases ( O1 c= O3 or O3 c= O1 ) ;

suppose O1 c= O3 ; :: thesis: q [= f,O1 +. a

then f,O3 +. a [= f,O1 +. a by A7, A8, A10;
hence q [= f,O1 +. a by A8, A10; :: thesis: verum

end;

suppose O3 c= O1 ; :: thesis: q [= f,O1 +. a

then f,O3 +. a [= f,O1 +. a by A1, Th27;
hence q [= f,O1 +. a by A8, A10; :: thesis: verum

end;

end;

end;

then A11: f,O2 +. a [= f,O1 +. a by A9, LATTICE3:def 21;
assume O1 c= O2 ; :: thesis: f,O1 +. a = f,O2 +. a
then f,O1 +. a [= f,O2 +. a by A1, Th27;
hence f,O1 +. a = f,O2 +. a by A11, LATTICES:26; :: thesis: verum

end;

end;

thus for O2 being Ordinal holds S₁[O2] from ORDINAL2:sch 1(A2, A3, A6); :: thesis: verum