# Lativity and interstitiality

Patrik Eklund peklund at cs.umu.se
Wed Mar 8 06:47:49 EST 2023

```Dear all,

Some of you may recall how I have used the word "lativity" in the
context of from-to constructions in logic. For instance, at the
beginning of logic constructions we start with the signature and from
there we can come to terms, and from there we come to sentences, and so
on. Important in doing so is that we always close the door behind us.
For instance, once we have terms, we fix that "object of all terms" when
we proceed to construct sentences based on terms, i.e., we cannot find a
new term and say "Oh! Here's a new one. Let's throw it in to whatever we
already had as terms.".

Maybe "lativity" is not the best word for that from-to and closing the
door behind you, but that is the word I have used.

The interstice in that from-to lativity is also important. From
signature to term, there is the actual interstitial construction of
terms. This can be done with a set-theoretic construction, with a mix of
set theory and category theory, and with a purely categorical
construction of terms, also in the many-sorted case, and even over any
monoidal closed category apart from the category of sets and functions.
Of course, in the monoidal cat case, "terms" are not what they usually
look like, and often we simply have the "object of all terms". However,
there are some categories, like the Goguen category for "fuzzy sets",
either over a distributive lattice, or over quantales. In that
particular Goguen case, terms are "many-valued" terms so that even
operators are many-valued. So, in a simple example, if the result of 2+2
is uncertain, it may not be just about the uncertainty of 2 but indeed
also about the uncertainty of +. This "terms over Goguen's category" can
also be done for lambda terms, where the underlying signature can be
arranged so that the function type constructor is an operator (on a
certain level) and even application can be arranged as an operator.
Application can then be "uncertain". I would be curious to see what
Wolfram's trees would look like with such terms.

What I try to say is that whenever we aim at being very constructive in
those interstices we may open up views of things we may not have seen
before while dealing with those interstices in more intuitive ways.

Similarly, I'm not sure "interstitiality" is the best word for this
particular thing. I am perhaps inspired by the so called interstitial
cells of Cajal (ICC) e.g. in the gastrointestinal tract. They are
myenteric and they also have a certain pace making role in the
intestines. The neuron has provided inspiration for neural networks, so
maybe those ICCs could have some relations in that "lativity" and
interstitiality" of logic and logical constructions from-to.

The above is more of gut feelings than computations or mathematics above
my spine, and I didn't check what ChatGPT would say about this.

Best,

Patrik
```

More information about the FOM mailing list