IsarMathLib

Proofs by humans, for humans, formally verified by Isabelle/ZF proof assistant

theory Order_ZF_1 imports ZF.Order ZF1

begin

In Order_ZF we define some notions related to order relations based on the nonstrict orders ( $\leq$ type). Some people however prefer to talk about these notions in terms of the strict order relation ( $<$ type). This is the case for the standard Isabelle Order.thy and also for Metamath. In this theory file we repeat some developments from Order_ZF using the strict order relation as a basis.This is mostly useful for Metamath translation, but is also of some general interest. The names of theorems are copied from Metamath.

Definitions and basic properties

In this section we introduce some definitions taken from Metamath and relate them to the ones used by the standard Isabelle Order.thy.

The next definition is the strict version of the linear order. What we write as R Orders A is written $R O r d A$ in Metamath.

definition

$R orders A \equiv \forall x y z . (x \in A \land y \in A \land z \in A) ⟶$ $(⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)) \land$ $(⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R)$

The definition of supremum for a (strict) linear order.

definition

$Sup (B, A, R) \equiv$ $⋃ {x \in A . (\forall y \in B . ⟨ x, y ⟩ \notin R) \land$ $(\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))}$

Definition of infimum for a linear order. It is defined in terms of supremum.

definition

$Infim (B, A, R) \equiv Sup (B, A, c o n v e r s e (R))$

If relation $R$ orders a set $A$ , (in Metamath sense) then $R$ is irreflexive, transitive and linear therefore is a total order on $A$ (in Isabelle sense).

lemma orders_imp_tot_ord:

assumes A1: $R orders A$

shows

i r refl (A, R)

t r a n s [A] (R)

p a r t_o r d (A, R)

l i n e a r (A, R)

t o t_o r d (A, R)

proof

from A1 have I:

\forall x y z . (x \in A \land y \in A \land z \in A) ⟶

(⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)) \land

(⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R)

unfolding StrictOrder_def

then have

\forall x \in A . ⟨ x, x ⟩ \notin R

then show

i r refl (A, R)

using irrefl_def

moreover

from I have

\forall x \in A . \forall y \in A . \forall z \in A . ⟨ x, y ⟩ \in R ⟶ ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R

then show

t r a n s [A] (R)

unfolding trans_on_def

ultimately show

p a r t_o r d (A, R)

using part_ord_def

moreover

from I have

\forall x \in A . \forall y \in A . ⟨ x, y ⟩ \in R \lor x = y \lor ⟨ y, x ⟩ \in R

then show

l i n e a r (A, R)

unfolding linear_def

ultimately show

t o t_o r d (A, R)

using tot_ord_def

qed

A converse of orders_imp_tot_ord. Together with that theorem this shows that Metamath's notion of an order relation is equivalent to Isabelles tot_ord predicate.

lemma tot_ord_imp_orders:

assumes A1: $t o t_o r d (A, R)$

shows

R orders A

proof

from A1 have I:

l i n e a r (A, R)

and II:

i r refl (A, R)

and III:

t r a n s [A] (R)

and IV:

p a r t_o r d (A, R)

using tot_ord_def, part_ord_def

from IV have

a s y m (R \cap A \times A)

using part_ord_Imp_asym

then have V:

\forall x y . ⟨ x, y ⟩ \in (R \cap A \times A) ⟶ \neg (⟨ y, x ⟩ \in (R \cap A \times A))

unfolding asym_def

from I have VI:

\forall x \in A . \forall y \in A . ⟨ x, y ⟩ \in R \lor x = y \lor ⟨ y, x ⟩ \in R

unfolding linear_def

from III have VII:

\forall x \in A . \forall y \in A . \forall z \in A . ⟨ x, y ⟩ \in R ⟶ ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R

unfolding trans_on_def

{

fix

x

y

z

assume T:

x \in A

y \in A

z \in A

have

⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)

proof

assume A2:

⟨ x, y ⟩ \in R

with V, T have

\neg (⟨ y, x ⟩ \in R)

moreover

from II, T, A2 have

x \neq y

using irrefl_def

ultimately show

\neg (x = y \lor ⟨ y, x ⟩ \in R)

next

assume

\neg (x = y \lor ⟨ y, x ⟩ \in R)

with VI, T show

⟨ x, y ⟩ \in R

qed

moreover

from VII, T have

⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R

ultimately have

(⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)) \land

(⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R)

}

then have

\forall x y z . (x \in A \land y \in A \land z \in A) ⟶

(⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)) \land

(⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R)

then show

R orders A

using StrictOrder_def

qed

Properties of (strict) total orders

In this section we discuss the properties of strict order relations. This continues the development contained in the standard Isabelle's Order.thy with a view towards using the theorems translated from Metamath.

A relation orders a set iff the converse relation orders a set. Going one way we can use the the lemma tot_od_converse from the standard Isabelle's Order.thy.The other way is a bit more complicated (note that in Isabelle for $c o n v e r s e (c o n v e r s e (r)) = r$ one needs $r$ to consist of ordered pairs, which does not follow from the StrictOrder definition above).

lemma cnvso:

shows

R orders A ⟷ c o n v e r s e (R) orders A

proof

let

r = c o n v e r s e (R)

assume

R orders A

then have

t o t_o r d (A, r)

using orders_imp_tot_ord, tot_ord_converse

then show

r orders A

using tot_ord_imp_orders

next

let

r = c o n v e r s e (R)

assume

r orders A

then have A2:

\forall x y z . (x \in A \land y \in A \land z \in A) ⟶

(⟨ x, y ⟩ \in r ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in r)) \land

(⟨ x, y ⟩ \in r \land ⟨ y, z ⟩ \in r ⟶ ⟨ x, z ⟩ \in r)

using StrictOrder_def

{

fix

x

y

z

assume

x \in A \land y \in A \land z \in A

with A2 have I:

⟨ y, x ⟩ \in r ⟷ \neg (x = y \lor ⟨ x, y ⟩ \in r)

and II:

⟨ y, x ⟩ \in r \land ⟨ z, y ⟩ \in r ⟶ ⟨ z, x ⟩ \in r

from I have

⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)

moreover

from II have

⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R

ultimately have

(⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)) \land

(⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R)

}

then have

\forall x y z . (x \in A \land y \in A \land z \in A) ⟶

(⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)) \land

(⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R)

then show

R orders A

using StrictOrder_def

qed

Supremum is unique, if it exists.

lemma supeu:

assumes A1: $R orders A$ and A2: $x \in A$ and A3: $\forall y \in B . ⟨ x, y ⟩ \notin R$ and A4: $\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R)$

shows

\exists! x . x \in A \land (\forall y \in B . ⟨ x, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))

proof

from A2, A3, A4 show

\exists x . x \in A \land (\forall y \in B . ⟨ x, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))

next

fix

x_{1}

x_{2}

assume A5:

x_{1} \in A \land (\forall y \in B . ⟨ x_{1}, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x_{1} ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))

x_{2} \in A \land (\forall y \in B . ⟨ x_{2}, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x_{2} ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))

from A1 have

l i n e a r (A, R)

using orders_imp_tot_ord, tot_ord_def

then have

\forall x \in A . \forall y \in A . ⟨ x, y ⟩ \in R \lor x = y \lor ⟨ y, x ⟩ \in R

unfolding linear_def

with A5 have

⟨ x_{1}, x_{2} ⟩ \in R \lor x_{1} = x_{2} \lor ⟨ x_{2}, x_{1} ⟩ \in R

moreover {

assume

⟨ x_{1}, x_{2} ⟩ \in R

with A5 obtain

z

where

z \in B

and

⟨ x_{1}, z ⟩ \in R

with A5 have

F a l s e

} moreover {

assume

⟨ x_{2}, x_{1} ⟩ \in R

with A5 obtain

z

where

z \in B

and

⟨ x_{2}, z ⟩ \in R

with A5 have

F a l s e

} ultimately show

x_{1} = x_{2}

qed

Supremum has expected properties if it exists.

lemma sup_props:

assumes A1: $R orders A$ and A2: $\exists x \in A . (\forall y \in B . ⟨ x, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))$

shows

Sup (B, A, R) \in A

\forall y \in B . ⟨ Sup (B, A, R), y ⟩ \notin R

\forall y \in A . ⟨ y, Sup (B, A, R) ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R)

proof

let

S = {x \in A . (\forall y \in B . ⟨ x, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))}

from A2 obtain

x

where

x \in A

and

(\forall y \in B . ⟨ x, y ⟩ \notin R)

and

\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R)

with A1 have I:

\exists! x . x \in A \land (\forall y \in B . ⟨ x, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))

using supeu

then have

(⋃ S) \in A

by (rule ZF1_1_L9 )

then show

Sup (B, A, R) \in A

using Sup_def

from I have II:

(\forall y \in B . ⟨ ⋃ S, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, ⋃ S ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))

by (rule ZF1_1_L9 )

hence

\forall y \in B . ⟨ ⋃ S, y ⟩ \notin R

moreover

have III:

(⋃ S) = Sup (B, A, R)

using Sup_def

ultimately show

\forall y \in B . ⟨ Sup (B, A, R), y ⟩ \notin R

from II have IV:

\forall y \in A . ⟨ y, ⋃ S ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R)

{

fix

y

assume A3:

y \in A

and

⟨ y, Sup (B, A, R) ⟩ \in R

with III have

⟨ y, ⋃ S ⟩ \in R

with IV, A3 have

\exists z \in B . ⟨ y, z ⟩ \in R

}

thus

\forall y \in A . ⟨ y, Sup (B, A, R) ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R)

qed

Elements greater or equal than any element of $B$ are greater or equal than supremum of $B$ .

lemma supnub:

assumes A1: $R orders A$ and A2: $\exists x \in A . (\forall y \in B . ⟨ x, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))$ and A3: $c \in A$ and A4: $\forall z \in B . ⟨ c, z ⟩ \notin R$

shows

⟨ c, Sup (B, A, R) ⟩ \notin R

proof

from A1, A2 have

\forall y \in A . ⟨ y, Sup (B, A, R) ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R)

by (rule sup_props )

with A3, A4 show

⟨ c, Sup (B, A, R) ⟩ \notin R

qed

end

Definition of StrictOrder:

R orders A \equiv \forall x y z . (x \in A \land y \in A \land z \in A) ⟶

(⟨ x, y ⟩ \in R ⟷ \neg (x = y \lor ⟨ y, x ⟩ \in R)) \land

(⟨ x, y ⟩ \in R \land ⟨ y, z ⟩ \in R ⟶ ⟨ x, z ⟩ \in R)

lemma orders_imp_tot_ord:

assumes $R orders A$

shows

i r refl (A, R)

t r a n s [A] (R)

p a r t_o r d (A, R)

l i n e a r (A, R)

t o t_o r d (A, R)

lemma tot_ord_imp_orders:

assumes $t o t_o r d (A, R)$

shows

R orders A

lemma supeu:

assumes $R orders A$ and $x \in A$ and $\forall y \in B . ⟨ x, y ⟩ \notin R$ and $\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R)$

shows

\exists! x . x \in A \land (\forall y \in B . ⟨ x, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))

lemma ZF1_1_L9:

assumes $\exists! x . x \in A \land ϕ (x)$

shows

\exists a . {x \in A . ϕ (x)} = {a}

⋃ {x \in A . ϕ (x)} \in A

ϕ (⋃ {x \in A . ϕ (x)})

\exists x \in A . ϕ (x)

Definition of Sup:

Sup (B, A, R) \equiv

⋃ {x \in A . (\forall y \in B . ⟨ x, y ⟩ \notin R) \land

(\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))}

lemma sup_props:

assumes $R orders A$ and $\exists x \in A . (\forall y \in B . ⟨ x, y ⟩ \notin R) \land (\forall y \in A . ⟨ y, x ⟩ \in R ⟶ (\exists z \in B . ⟨ y, z ⟩ \in R))$