differential propositional calculus

differential propositional calculus

A

differential propositional calculus

is a

propositional calculus

(

http://

planetmath

.org/PropositionalCalculus

) extended by a set of terms for describing aspects of change and

difference

, for example, processes that take place in a

universe of discourse

or

transformations

that map a source universe into a target universe.

Contents:

1

Casual introduction

2

Cactus calculus

3

Formal development

3.1

Elementary notions

3.2

Special classes of propositions

3.3

Differential extensions

1

Casual introduction

Consider the situation represented by the

venn diagram

in Figure 1.

Figure

1

.

Local Habitations, And Names

The area of the

rectangle

represents a universe of discourse,

X

.

This might be a population of

individuals

having various additional

properties

or it might be a

collection

of locations that various individuals occupy. The area of the “circle” represents the individuals that have the property

q

or the locations that fall within the corresponding region

Q

.

Four individuals,

a

,

b

,

c

,

d

,

are singled out by name. It happens that

b

and

c

currently reside in region

Q

while

a

and

d

do not.

Now consider the situation represented by the venn diagram in Figure 2.

Figure

2

.

Same Names, Different Habitations

Figure 2 differs from Figure 1 solely in the circumstance that the object

c

is outside the region

Q

while the object

d

is inside the region

Q

.

So far, there is nothing that says that our encountering these Figures in this order is other than purely accidental, but if we interpret the present

sequence

of frames as a “moving picture”

representation

of their natural order in a temporal process, then it would be natural to say that

a

and

b

have remained as they were with regard to quality

q

while

c

and

d

have changed their standings in that respect. In particular,

c

has moved from the region where

q

is

true

to the region where

q

is

false

while

d

has moved from the region where

q

is

false

to the region where

q

is

𝑡𝑟𝑢𝑒

.

Figure 1

′

reprises the situation shown in Figure 1, but this time interpolates a new quality that is specifically tailored to account for the

relation

between Figure 1 and Figure 2.

Figure

1

′

.

Back, To The Future

This new quality,

d

⁡

q

,

is an example of a

differential quality

, since its absence or presence qualifies the absence or presence of change occurring in another quality. As with any other quality, it is represented in the venn diagram by means of a “circle” that distinguishes two halves of the universe of discourse, in this case, the portions of

X

outside and inside the region

d

⁡

Q

.

Figure 1 represents a universe of discourse,

X

,

together with a basis of discussion,

{

q

}

,

for expressing

propositions

about the contents of that

universe

. Once the quality

q

is given a name, say, the symbol

`

⁢

`

⁢

q

⁢

"

, we have a basis for a

formal language

that is specifically cut out for discussing

X

in terms of

q

,

and this formal language is more formally known as the

propositional calculus

with

alphabet

{

`

⁢

`

⁢

q

⁢

"

}

.

In the

context

marked by

X

and

{

q

}

there are but four different pieces of

information

that can be expressed in the corresponding propositional calculus, namely, the propositions:

𝑓𝑎𝑙𝑠𝑒

,

¬

⁢

q

,

q

,

𝑡𝑟𝑢𝑒

.

Referring to the sample of points in Figure 1,

false

holds of no points,

¬

⁢

q

holds of

a

and

d

,

q

holds of

b

and

c

, and

true

holds of all points in the sample.

Figure

1

′

preserves

the same universe of discourse and extends the basis of discussion to a set of two qualities,

{

q

,

d

⁡

q

}

.

In

parallel

fashion, the initial propositional calculus is extended by means of the enlarged alphabet,

{

`

⁢

`

⁢

q

⁢

"

,

`

⁢

`

⁢

d

⁡

q

⁢

"

}

.

Any propositional calculus over two basic propositions allows for the

expression

of 16 propositions all together. Just by way of salient examples in the present setting, we can pick out the most informative propositions that apply to each of our sample points. Using overlines to express logical

negation

, these are given as follows:

•

q

¯

⁢

d

⁡

q

¯

describes

a

•

q

¯

⁢

d

⁡

q

describes

d

•

q

⁢

d

⁡

q

¯

describes

b

•

q

⁢

d

⁡

q

describes

c

Table 3 exhibits the

rules of inference

that give the differential quality

d

⁡

q

its meaning in practice.

Table 3. Differential Inference Rules

From

q

¯

and

d

⁡

q

¯

infer

q

¯

next.

From

q

¯

and

d

⁡

q

infer

q

next.

From

q

and

d

⁡

q

¯

infer

q

next.

From

q

and

d

⁡

q

infer

q

¯

next.

2

Cactus calculus

Table 4 outlines a syntax for propositional calculus based on two types of

logical connectives

, both of

variable

k

-ary scope.

•

A bracketed list of propositional expressions in the form

(

e

1

,

e

2

,

…

,

e

k

-

1

,

e

k

)

indicates that exactly one of the propositions

e

1

,

e

2

,

…

,

e

k

-

1

,

e

k

is false.

•

A

concatenation

of propositional expressions in the form

e

1

⁢

e

2

⁢

…

⁢

e

k

-

1

⁢

e

k

indicates that all of the propositions

e

1

,

e

2

,

…

,

e

k

-

1

,

e

k

are true, in other words, that their logical conjunction is true.

Table 4. Syntax and

Semantics

of a Propositional Calculus

Expression

Interpretation

Other Notations

True

1

(

)

False

0

x

x

x

(

x

)

Not

⁡

x

x

′

x

~

¬

⁢

x

x

⁢

y

⁢

z

x

⁢

and

⁡

y

⁢

and

⁡

z

x

∧

y

∧

z

(

(

x

)

⁢

(

y

)

⁢

(

z

)

)

x

⁢

or

⁡

y

⁢

or

⁡

z

x

∨

y

∨

z

(

x

⁢

(

y

)

)

x

⁢

implies

⁡

y

If

⁡

x

⁢

then

⁡

y

x

⇒

y

(

x

,

y

)

x

⁢

not

⁢

equal

⁢

to

⁡

y

x

⁢

exclusive

⁢

or

⁡

y

x

≠

y

x

+

y

(

(

x

,

y

)

)

x

⁢

is

⁢

equal

⁢

to

⁡

y

x

⁢

if

⁢

and

⁢

only

⁢

if

⁡

y

x

=

y

x

⇔

y

(

x

,

y

,

z

)

Just

⁢

one

⁢

of

x

,

y

,

z

is

⁢

false

.

x

′

⁢

y

⁢

z

∨

x

⁢

y

′

⁢

z

∨

x

⁢

y

⁢

z

′

(

(

x

)

,

(

y

)

,

(

z

)

)

Just

⁢

one

⁢

of

x

,

y

,

z

is

⁢

true

.

Partition

⁢

all

into

⁡

x

,

y

,

z

.

x

⁢

y

′

⁢

z

′

∨

x

′

⁢

y

⁢

z

′

∨

x

′

⁢

y

′

⁢

z

(

(

x

,

y

)

,

z

)

(

x

,

(

y

,

z

)

)

Oddly

⁢

many

⁢

of

x

,

y

,

z

are

⁢

true

.

x

+

y

+

z

=

x

⁢

y

⁢

z

∨

x

⁢

y

′

⁢

z

′

∨

x

′

⁢

y

⁢

z

′

∨

x

′

⁢

y

′

⁢

z

(

w

,

(

x

)

,

(

y

)

,

(

z

)

)

Partition

⁡

w

into

⁡

x

,

y

,

z

.

Genus

⁡

w

⁢

comprises

species

⁡

x

,

y

,

z

.

w

′

⁢

x

′

⁢

y

′

⁢

z

′

∨

w

⁢

x

⁢

y

′

⁢

z

′

∨

w

⁢

x

′

⁢

y

⁢

z

′

∨

w

⁢

x

′

⁢

y

′

⁢

z

All other

propositional connectives

can be obtained through

combinations

of these two forms.

Strictly

speaking, the concatenation form is dispensable in light of the bracket form, but it is convenient to maintain it as an abbreviation of more complicated bracket expressions. The briefest expression for logical truth is the

empty word

, abstractly denoted

ε

or

λ

in formal languages, where it forms the

identity element

for concatenation. It can be given visible expression in this context by means of the

logically equivalent

expression

`

⁢

`

⁢

(

(

)

)

⁢

"

,

or, especially if operating in an algebraic context, by a simple

`

⁢

`

⁢

1

⁢

"

.

Also when working in an algebraic mode, the

plus sign

`

⁢

`

+

"

may be used for

exclusive disjunction

. For example, we have the following paraphrases of algebraic expressions by bracket expressions:

x

+

y

=

(

x

,

y

)

x

+

y

+

z

=

(

(

x

,

y

)

,

z

)

=

(

x

,

(

y

,

z

)

)

It is important to note that the last expressions are not

equivalent

to the triple bracket

(

x

,

y

,

z

)

.

For more information about this syntax for propositional calculus, see the entries on

minimal negation operators

(

http://planetmath.org/MinimalNegationOperator

),

zeroth order logic

(

http://planetmath.org/ZerothOrderLogic

), and Table A1 in Appendix 1 (

http://planetmath.org/DifferentialPropositionalCalculusAppendices

).

3

Formal development

The preceding discussion outlined the ideas leading to the differential extension of propositional logic. The next task is to lay out the

concepts

and terminology that are needed to describe various orders of

differential

propositional calculi.

3.1

Elementary notions

Logical description of a universe of discourse begins with a set of logical signs. For the sake of

simplicity

in a first approach, assume that these logical signs are collected in the form of a finite alphabet,

𝔄

=

{

`

⁢

`

⁢

a

1

⁢

"

,

…

,

`

⁢

`

⁢

a

n

⁢

"

}

.

Each of these signs is interpreted as denoting a logical feature, for

instance

, a property that objects in the universe of discourse may have or a proposition about objects in the universe of discourse. Corresponding to the alphabet

𝔄

there is then a set of logical features,

𝒜

=

{

a

1

,

…

,

a

n

}

.

A set of logical features,

𝒜

=

{

a

1

,

…

,

a

n

}

,

affords a basis for generating an

n

-dimensional universe of discourse, written

A

∘

=

[

𝒜

]

=

[

a

1

,

…

,

a

n

]

.

It is useful to consider a universe of discourse as a

categorical

(

http://planetmath.org/Category

) object that incorporates both the set of points

A

=

⟨

a

1

,

…

,

a

n

⟩

and the set of propositions

A

↑

=

{

f

:

A

→

𝔹

}

that are implicit with the ordinary picture of a venn diagram on

n

features. Accordingly, the universe of discourse

A

∘

may be regarded as an

ordered pair

(

A

,

A

↑

)

having the type

(

𝔹

n

,

(

𝔹

n

→

𝔹

)

)

,

and this last type designation may be abbreviated as

𝔹

n

+

→

𝔹

,

or even more succinctly as

[

𝔹

n

]

.

For convenience, the data type of a

finite set

on

n

elements

may be indicated by either one of the equivalent notations,

[

n

]

or

𝐧

.

Table 5 summarizes the notations that are needed to describe ordinary propositional calculi in a systematic fashion.

Table 5. Propositional Calculus : Basic Notation

Symbol

Notation

Description

Type

𝔄

{

`

⁢

`

⁢

a

1

⁢

"

,

…

,

`

⁢

`

⁢

a

n

⁢

"

}

Alphabet

[

n

]

=

𝐧

𝒜

{

a

1

,

…

,

a

n

}

Basis

[

n

]

=

𝐧

A

i

{

a

i

¯

,

a

i

}

Dimension

i

𝔹

A

⟨

𝒜

⟩

Set of cells,

𝔹

n

⟨

a

1

,

…

,

a

n

⟩

coordinate

tuples,

{

(

a

1

,

…

,

a

n

)

}

points, or vectors

A

1

×

…

×

A

n

in the universe

∏

i

=

1

n

A

i

of discourse

A

*

(

hom

:

A

→

𝔹

)

Linear functions

(

𝔹

n

)

*

≅

𝔹

n

A

↑

(

A

→

𝔹

)

Boolean functions

𝔹

n

→

𝔹

A

∘

[

𝒜

]

Universe of discourse

(

𝔹

n

,

(

𝔹

n

→

𝔹

)

)

(

A

,

A

↑

)

based on the features

(

𝔹

n

+

→

𝔹

)

(

A

+

→

𝔹

)

{

a

1

,

…

,

a

n

}

[

𝔹

n

]

(

A

,

(

A

→

𝔹

)

)

[

a

1

,

…

,

a

n

]

3.2

Special classes of propositions

A

basic proposition

,

coordinate proposition

, or

simple proposition

in the universe of discourse

[

a

1

,

…

,

a

n

]

is one of the propositions in the set

{

a

1

,

…

,

a

n

}

.

Among the

2

2

n

propositions in

[

a

1

,

…

,

a

n

]

are several families of

2

n

propositions each that take on special forms with respect to the basis

{

a

1

,

…

,

a

n

}

.

Three of these families are especially prominent in the present context, the

linear

, the

positive

, and the

singular

propositions. Each family is naturally parameterized by the coordinate

n

-tuples in

𝔹

n

and falls into

n

+

1

ranks, with a

binomial coefficient

(

n

k

)

giving the number of propositions that have rank or weight

k

.

•

The

linear propositions

,

{

ℓ

:

𝔹

n

→

𝔹

}

=

(

𝔹

n

→

ℓ

𝔹

)

,

may be expressed as sums:

∑

i

=

1

n

e

i

=

e

1

+

…

+

e

n

where

e

i

=

a

i

or

e

i

=

0

for

⁡

i

=

1

⁢

to

⁡

n

.

•

The

positive propositions

,

{

p

:

𝔹

n

→

𝔹

}

=

(

𝔹

n

→

𝑝

𝔹

)

,

may be expressed as

products

:

∏

i

=

1

n

e

i

=

e

1

⋅

…

⋅

e

n

where

e

i

=

a

i

or

e

i

=

1

for

⁡

i

=

1

⁢

to

⁡

n

.

•

The

singular propositions

,

{

𝐱

:

𝔹

n

→

𝔹

}

=

(

𝔹

n

→

𝑠

𝔹

)

,

may be expressed as products:

∏

i

=

1

n

e

i

=

e

1

⋅

…

⋅

e

n

where

e

i

=

a

i

or

e

i

=

(

a

i

)

for

⁡

i

=

1

⁢

to

⁡

n

.

In each case the rank

k

ranges from

0

to

n

and counts the number of positive appearances of the coordinate propositions

a

1

,

…

,

a

n

in the resulting expression. For example, for

n

=

3

,

the linear proposition of rank

0

is

0

,

the positive proposition of rank

0

is

1

,

and the singular proposition of rank

0

is

(

a

1

)

⁢

(

a

2

)

⁢

(

a

3

)

.

The basic propositions

a

i

:

𝔹

n

→

𝔹

are both linear and positive. So these two kinds of propositions, the linear and the positive, may be viewed as two different ways of generalizing the class of basic propositions.

Finally, it is important to note that all of the above distinctions are relative to the choice of a particular logical basis

𝒜

=

{

a

1

,

…

,

a

n

}

.

For example, a singular proposition with respect to the basis

𝒜

will not remain singular if

𝒜

is extended by a number of new and

independent

features. Even if one keeps to the original set of pairwise options

{

a

i

}

∪

{

(

a

i

)

}

to pick out a new basis, the sets of linear propositions and positive propositions are both determined by the choice of basic propositions, and this whole determination is tantamount to the purely conventional choice of a cell as origin.

3.3

Differential extensions

An initial universe of discourse,

A

∘

, supplies the groundwork for any number of further

extensions

, beginning with the

first order

differential extension

,

E

⁡

A

∘

.

The construction of

E

⁡

A

∘

can be described in the following stages:

•

The initial alphabet,

𝔄

=

{

`

⁢

`

⁢

a

1

⁢

"

,

…

,

`

⁢

`

⁢

a

n

⁢

"

}

,

is extended by a

first order differential alphabet

,

d

⁡

𝔄

=

{

`

⁢

`

⁢

d

⁡

a

1

⁢

"

,

…

,

`

⁢

`

⁢

d

⁡

a

n

⁢

"

}

,

resulting in a

first order extended alphabet

,

E

⁡

𝔄

,

defined as follows:

E

⁡

𝔄

=

𝔄

∪

d

⁡

𝔄

=

{

`

⁢

`

⁢

a

1

⁢

"

,

…

,

`

⁢

`

⁢

a

n

⁢

"

,

`

⁢

`

⁢

d

⁡

a

1

⁢

"

,

…

,

`

⁢

`

⁢

d

⁡

a

n

⁢

"

}

.

•

The initial basis,

𝒜

=

{

a

1

,

…

,

a

n

}

,

is extended by a

first order differential basis

,

d

⁡

𝒜

=

{

d

⁡

a

1

,

…

,

d

⁡

a

n

}

,

resulting in a

first order extended basis

,

E

⁡

𝒜

,

defined as follows:

E

⁡

𝒜

=

𝒜

∪

d

⁡

𝒜

=

{

a

1

,

…

,

a

n

,

d

⁡

a

1

,

…

,

d

⁡

a

n

}

.

•

The initial space,

A

=

⟨

a

1

,

…

,

a

n

⟩

,

is extended by a

first order differential space

or

tangent space

,

d

⁡

A

=

⟨

d

⁡

a

1

,

…

,

d

⁡

a

n

⟩

,

at each point of

A

,

resulting in a

first order extended space

or

tangent bundle space

,

E

⁡

A

,

defined as follows:

E

⁡

A

=

A

×

d

⁡

A

=

⟨

E

⁡

𝒜

⟩

=

⟨

𝒜

∪

d

⁡

𝒜

⟩

=

⟨

a

1

,

…

,

a

n

,

d

⁡

a

1

,

…

,

d

⁡

a

n

⟩

.

•

Finally, the initial universe,

A

∘

=

[

a

1

,

…

,

a

n

]

,

is extended by a

first order differential universe

or

tangent universe

,

d

⁡

A

∘

=

[

d

⁡

a

1

,

…

,

d

⁡

a

n

]

,

at each point of

A

∘

,

resulting in a

first order extended universe

or

tangent bundle universe

,

E

⁡

A

∘

,

defined as follows:

E

⁡

A

∘

=

[

E

⁡

𝒜

]

=

[

𝒜

∪

d

⁡

𝒜

]

=

[

a

1

,

…

,

a

n

,

d

⁡

a

1

,

…

,

d

⁡

a

n

]

.

This gives

E

⁡

A

∘

the type:

[

𝔹

n

×

𝔻

n

]

=

(

𝔹

n

×

𝔻

n

+

→

𝔹

)

=

(

𝔹

n

×

𝔻

n

,

𝔹

n

×

𝔻

n

→

𝔹

)

.

A proposition in a differential extension of a universe of discourse is called a

differential proposition

and forms the analogue of a system of differential equations in ordinary calculus (

http://planetmath.org/Calculus

). With these constructions, the first order extended universe

E

⁡

A

∘

and the first order differential proposition

f

:

E

⁡

A

→

𝔹

,

we have arrived, in concept at least, at the foothills of differential logic.

Table 6 summarizes the notations that are needed to describe the first order differential extensions of propositional calculi in a systematic manner.

Table 6. Differential Extension : Basic Notation

Symbol

Notation

Description

Type

d

⁡

𝔄

{

`

⁢

`

⁢

d

⁡

a

1

⁢

"

,

…

,

`

⁢

`

⁢

d

⁡

a

n

⁢

"

}

Alphabet of differential symbols

[

n

]

=

𝐧

d

⁡

𝒜

{

d

⁡

a

1

,

…

,

d

⁡

a

n

}

Basis of differential features

[

n

]

=

𝐧

d

⁡

A

i

{

d

⁡

a

i

¯

,

d

⁡

a

i

}

Differential dimension

i

𝔻

d

⁡

A

⟨

d

⁡

𝒜

⟩

Tangent space at a point:

𝔻

n

⟨

d

⁡

a

1

,

…

,

d

⁡

a

n

⟩

Set of changes,

{

(

d

⁡

a

1

,

…

,

d

⁡

a

n

)

}

motions, steps,

d

⁡

A

1

×

…

×

d

⁡

A

n

tangent vectors

∏

i

=

1

n

d

⁡

A

i

at a point

d

⁡

A

*

(

hom

:

d

⁡

A

→

𝔹

)

Linear functions on

d

⁡

A

(

𝔻

n

)

*

≅

𝔻

n

d

⁡

A

↑

(

d

⁡

A

→

𝔹

)

Boolean functions on

d

⁡

A

𝔻

n

→

𝔹

d

⁡

A

∘

[

d

⁡

𝒜

]

Tangent universe

(

𝔻

n

,

(

𝔻

n

→

𝔹

)

)

(

d

⁡

A

,

d

⁡

A

↑

)

at a point of

A

∘

,

(

𝔻

n

+

→

𝔹

)

(

d

⁡

A

+

→

𝔹

)

based on the

[

𝔻

n

]

(

d

A

,

(

d

A

→

𝔹

)

)

tangent

features

[

d

⁡

a

1

,

…

,

d

⁡

a

n

]

{

d

⁡

a

1

,

…

,

d

⁡

a

n

}

Title

differential propositional calculus

Canonical

name

DifferentialPropositionalCalculus

Date of creation

2013-08-22 21:54:38

Last modified on

2013-08-22 21:54:38

Owner

Jon Awbrey (15246)

Last modified by

Jon Awbrey (15246)

Numerical id

69

Author

Jon Awbrey (15246)

Entry type

Definition

Classification

msc 53A40

Classification

msc 39A12

Classification

msc 34G99

Classification

msc 03B44

Classification

msc 03B42

Classification

msc 03B05

Synonym

differential extension of propositional calculus

Related topic

Derivation

Related topic

DifferentialField

Related topic

DifferentialGeometry

Related topic

DifferentialLogic

Related topic

FiniteDifference

Related topic

FiniteField

Related topic

MinimalNegationOperator

Related topic

PropositionalCalculus

Related topic

ZerothOrderLogic

Defines

differential basis

Defines

differential extension

Defines

differential feature

Defines

differential inference

Defines

differential proposition

Defines

differential quality

Defines

differential variable

Defines

logical transformation

Defines

source universe

Defines

target universe

Defines

tangent universe

Defines

basic proposition

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