Re: Animated Logical Graphs • 21
Re: Ontolog Forum • Joseph Simpson
- JS:
- I tend to view equivalence and distinction as relationships as opposed to operations. I do not know if this makes any significant difference in this context.
Dear Joe,
I invoked the general concepts of equivalence and distinction at this point in order to keep the wider backdrop of ideas in mind but since we’ve been focusing on boolean functions to coordinate the semantics of propositional calculi we can get a sense of the links between operations and relations by looking at their relationship in a boolean frame of reference.
Let and
a positive integer. Then
is the set of
-tuples of elements of
- A
-variable boolean function is a mapping
- A
-place boolean relation is a subset of
The correspondence between boolean functions and boolean relations may be articulated as follows.
- Any
-place relation
as a subset of
has a corresponding indicator function (or characteristic function)
defined by the rule that
if
is in
and
if
is not in
- Any
-variable function
is the indicator function of a
-place relation
consisting of all the
in
where
The set
is called the fiber of
or the pre-image of
in
and is commonly notated as
Resources
- Logic Syllabus • Relation Theory
- Logical Equality • Logical Inequality
- Boolean Function • Boolean-Valued Function
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