Harold R. (Hal)
Foster’s Prince Valiant
© Respective
copyright/trademark holders.
If R is any relation, the converse of R is the
relation which holds between y and x whenever R holds between x and y. Thus greater is the converse of less, before of after, cause of effect, husband of wife, etc. The converse of R is written*1 CnvʻR
or R˘.
The definition is R˘= x^,y^(yRx) Df,
CnvʻR = R˘ Df.
The second of these is not a formally correct
definition, since we ought to define "Cnv"
and deduce the meaning of CnvʻR. But it is not
worthwhile to adopt this plan in our present introductory account, which aims
at simplicity rather than formal correctness.
A relation is called symmetrical if R = R, i.e.
if it holds between y and x whenever it holds between x and y (and therefore vice versa). Identity, diversity, agreement or disagreement in any respect,
are symmetrical relations. A relation is called asymmetrical when it is incompatible with its converse, i.e. when R ⩀ R˘
= L, or, what is equivalent,
xRy . Éx,y . ~(yRx).
Before and after,
greater and less, ancestor and descendant, are asymmetrical, as are all
other relations of the sort that lead to series.
But there are many asymmetrical relations which do not lead to series; for
instance, that of a wife's brother*2. A relation may be neither symmetrical nor
asymmetrical; for example, this holds of the relation of inclusion between
classes: a ⊂ b, and, b ⊂ a will both be
true if a = b, but otherwise
only one of them, at most, will be true. The relation brother is neither symmetrical nor asymmetrical, for if x is the brother of y, y may be either the brother or the sister of x.
In the propositional function xRy, we call x the referent and y the relatum. The class x^(xRy), consisting of all the x's which have the relation R to y,
is called the class of referents of y
with respect to R; the class x^(xRy),
consisting of all the y's to which x has the relation R, is called the class of relata of x with respect to R.
These two classes are denoted respectively by Rʻy⃗ and Rʻx ⃖. Thus
Rʻy⃗ = x^(xRy) Df,
Rʻx⃖ = y^(Rx)
Df.
The arrow runs towards y in the first case, to show that we are concerned with things
having the relation R to y; it runs away from x in the second case to show that the
relation R goes from x to the members of Rʻx. It runs in fact from a referent and towards a
relatum.
The notations Rʻy⃗, Rʻx⃖ are very
important, and are used constantly. If R
is the relation of parent to child, Rʻy = the parents of y,
Rʻx = the children of x. We have
┠ : x Î Rʻy. ≡ . xRy
and ┠ : y Î Rʻx. ≡ . xRy.
These equivalences are often embodied in
common language. For example, we say indiscriminately "x is an inhabitant of London" or
"x inhabits London." If we
put "R" for
"inhabits," "x
inhabits London" is "x R
London," while "x is an
inhabitant of London "is " x
Î R' London."
Instead of R⃗
and R⃖
we sometimes use sgʻR, gsʻR,
where "sg" stands for "sagitta," and "gs" is
" sg" backwards. Thus we put
sgʻR = R⃗ Df,
gsʻR = R⃖ Df.
These notations are sometimes more convenient than an
arrow when the relation concerned is represented by a combination of letters,
instead of a single letter such as R.
Thus e.g. we should write sgʻ(R ⍝ S), rather than put an arrow over the
whole length of (R ⍝ S).
The class of all terms that have the relation R to something or other is called the
domain of R. Thus if R is the relation of parent and child,
the domain of R will be the class of
parents. We represent the domain of R
by "DʻR." Thus we put
DʻR = x^{(∃y)
. xRy} Df.
*1 the
second of these notations is taken from Schroder's Algebra und Logik der
Relative. R. & W. 3
*2 this
relation is not strictly asymmetrical, but is so except when the wife's brother
is also the sister's husband. In the Greek Church the relation is strictly
asymmetrical.
Script: J Thomas Art: W Mortimer,
M Esposito © Respective copyright/trademark holders.
|
asymmetry in relations is one of the most complex and difficult aspects of our system examined so far. These may or may not affect a given proposition, or propositional equation, but it is helpful to understand that symmetry and asymmetry exists in these aspects, because failure to do so may occasionally lead us to error.
As I began studying Principia Mathematica the following
proposition immediately leapt out at me as applicable to all human
interactions.
┠ . (x)
. x = x
or, I assert “x is
true of all values of x = equals x.” or “everything equals itself.” as a
definite proposition. This led me to devise my very first propositional equation as follows
given:
φ = the class of all
persons as individuals
x^
= the expression denoting each individual’s intelligence
φx^ = expresses the set (x^1, x^2, …x^n) containing the aggregate representing each human being’s
intelligence
x^ = . ~∞. = each person’s
intelligence is less than infinite since each
person’s intelligence is ~∞ it follows
┠ . (x) . φx^ = . ~∞
or my definite assertion that no person can rightly be seen more intelligent than another person. I call this Comic Book Shaman’s Infinite
Intelligence theorem. This is a fine tool to demonstrate the essential function
of our system. You may agree or disagree with my theorem’s conclusion, you
may have made a thousand observations that seem to prove without question that
in your experience its opposite must be true. But this assertion, and all
assertions that follow are not determined by truth or falsehood; only that they
will never be proven in error.
James Childress’ Conchy ©Respective copyright/trademark holders.
|
Harold R. (Hal)
Foster’s Prince Valiant
© Respective
copyright/trademark holders.
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