Proof of "Axioms" of Propositional Logic:

Synopsis.

Willem F. Esterhuyse.

Abstract.

We introduce more basic axioms with which we are able to prove some

"axioms" of Propositional Logic. We use the symbols from my other article:

"Introduction to Logical Structures". Logical Structures (SrL) are graphs with

doubly labelled vertices with edges carrying symbols. The proofs are very

mechanical and does not require ingenuity to construct. It is easy to see that in

order to transform information, it has to be chopped up. Just look at a kid playing

with blocks with letters on them: he has to break up the word into letters to

assemble another word. Within SrL we take as our "atoms" propositions with

chopped up relations attached to them. We call the results: (incomplete)

"structures". We play it safe by allowing only relations among propositions to be

choppable. We will see whether this is the correct way of chopping up sentences

(it seems to be). This is where our Attractors (Repulsors) and Stoppers come in.

Attractors that face away from each other repels and so break a relation between

the two propositions. Then a Stopper attaches to the chopped up relation to

indicate it can't reconnect. So it is possible to infer sentences from sentences. The

rules I stumbled upon, to implement this, seems to be consistent. Sources differ

as to the axioms they choose but some of the most famous "axioms" are proved.

Modus Ponens occurs in all systems.

1. Introduction.

We use new operators called "Attractors" and "Stoppers". An Attractor ( symbol:

"-(" OR ")-") is an edge with a half circle symbol, that can carry any relation

symbol. Axioms for Attractors include A:AA (Axiom: Attractor Annihilation)

where we have as premise two structures named B with Attractors carrying the

"therefore" symbol facing each other and attached to two neighboring structures:

B. Because the structures are the same and the Attractors face each other, and the

therefore symbols point in the same direction, they annihilate the structures B and

we are left with a conclusion of the empty structure. Like in:

((B)->-( )->-(B)) <-> (Empty Structure).

where "<->" means: "is equivalent to" or "follows from and vice versa".

A:AD reads as follows:

((A)->-(B))->-( <-> )->-(A) []->-(B)->-(

where "[]->-" is a Stopper carrying "therefore" relation.

We also have the axiom: A:AtI (Attractor Introduction) in which we have a row

of structures as premise and conclusion of the same row of structures each with an

Attractor attached to them and pointing to the right or left. Like in:

A B C D <-> (A)-( (B)-( (C)-( (D)-(

OR:

A B C D <-> )-(A) )-(B) )-(C) )-(D)

where the Attractors may carry a relation symbol.

Further axioms are: A:SD says that we may drop a Stopper at either end of a line.

And A:ASS says we can exchange Stoppers for Attractors (and vice versa) in a

line of structures as long as we replace every instance of the operators. A:AL says

we can link two attractors pointing throwards each other and attached to two

different structures.

We prove Modus Ponens as follows:

Line nr. Statement Reason

1 B B -> C Premise

2 (B)->-( (B -> C)->-( 1, A:AtI

3 (B)->-( )->-(B) []->-(C)->-( 2, A:AD

4 []->-(C)->-( 3, A:AA

5 (C)->-( 4, A:SD

6 (C)->-[] 5, A:ASS

7 C 6, A:SD

We see that the Attractors cuts two structures into three (line 2 to line 3). In 2 "(B -> C)" is a structure.

We can prove AND-elimination, AND-introduction and transposition. We prove

Theorem: AND introduction (T:ANDI):

1 A B Premise

2 A -(x)-( B -(x)-( 1, A:AtI

3 (A)-(x)-[] (B)-(x)-[] 2, A:ASS

4 (A)-(x)-[] B 3, A:SD

5 (A)-(x)-( B 4, A:ASS

6 (A)-(x)-(B) 5, T:AL

where "-(x)-" = "AND", and T:AL is a theorem to be proved by reasoning

backwards through:

1 A -(x)- B Premise

2 A -(x)- B -(x)-( 1, A:AtI

3 )-(x)-(A) []-(x)-(B)-(x)-( 2, A:AD

4 []-(x)-(A) )-(x)-(B)-(x)-[] 3, A:ASS

5 A )-(x)-(B) 4, A:SD.

where the mirror image of this is proved similarly (by choosing to place the

Stopper on the other side of "-(x)-").

Modus Tollens and Syllogism can also be proven with these axioms.

We prove: Theorem (T:O): (A OR A) -> A:

1 A -(+)- A Premise

2 A -(+)- A -(+)-( 1, A:AtI

3 )-(+)-(A) []-(+)-(A)-(+)-( 2, A:AD

4 []-(+)-(A) )-(+)-(A)-(+)-[] 3, A:ASS

5 A )-(+)-(A) 4, A:SDx2

6 A []-(+)-(A) 5, A:ASS

and from this (on introduction of a model taking only structures with truth tables

as real) we can conclude that A holds as required (structure A with a Stopper attached

to it does not have a truth table associated with it).

We prove Syllogism:

1 A -> B B -> C Premise

2 (A -> B)->-( (B -> C)->-( 1, A:AtI

3 )->-(A)->-[] (B)->-( )->-(B) []->-(C)->-( 2, A:ADx2

4 (A)->-[] (B)->-( )->-(B) []->-(C) 3, A:ASS, A:SDx2, A:ASS

5 (A)->-[] []->-(C) 4, A:AA

6 (A)->-( )->-(C) 5, A:ASS

7 A -> C 6, A:AL