# [FOM] 658: Definitional Complexity Theory 2

Harvey Friedman hmflogic at gmail.com
Mon Feb 15 05:28:05 EST 2016

```The quantities associated with the expected definitional complexity of
"being a transitive set" given in
http://www.cs.nyu.edu/pipermail/fom/2016-February/019515.html were
wrong. This was a silly oversight on my part.

We expect

1. The variable complexity of transitivity to be 9 (not 8). Obviously,
it is <= 9.
2. The prefix complexity to be AAA. Obviously, it can be written in AAA.

It looks best to focus on just these two complexity notions: variable
complexity (the total number of occurrences of variables), and prefix
complexity.

I am not sure if anyone has analyzed the complexity of transitivity in
this sense; i.e., of transitive set.

What about "y is the power set of x"? We expect

1. The variable complexity of being the power set to be by (for all
z)(z in y iff z containedin x), which is 8.
2. The prefix complexity being the power set to be AAE and AEA.

These should be on the list to consider:

y = {x}
y = {{x}}
z = {x,y}
z = {{x},{x,y}}.
z is the Cartesian product of x,y.
x is a function.
x is a one-one function.
x is a function from y into z.
x = omega.
x is an ordinal.
x,y are equinumerous.
etcetera

These are in set theory only, as is motivated by automated theorem
proving. A related definitional complexity project(s) in other
contexts was discussed in
http://www.cs.nyu.edu/pipermail/fom/2015-January/018517.html

It would appear that some new interesting powerful tools need to be
developed in order to satisfactorily manage such a complexity theory.
We expect that the use of computers will be required, at least for
variable complexity calculations and estimates.

Is our usual intuition about the most economical ways of defining such
basic notions reasonably valid?

Of course, we can greatly expand this investigation, even within the
set theory framework, by allowing more than epsilon,=. We could
construct various replacements for just epsilon,= based, say, on the
frequency of use in mathematical papers. Then we can explore the
complexities of more complex mathematical notions (of a fundamental
character) over these stronger sets of primitives.

**********************************************************
My website is at https://u.osu.edu/friedman.8/ and my youtube site is at
This is the 658th in a series of self contained numbered
postings to FOM covering a wide range of topics in f.o.m. The list of
previous numbered postings #1-599 can be found at the FOM posting
http://www.cs.nyu.edu/pipermail/fom/2015-August/018887.html

600: Removing Deep Pathology 1  8/15/15  10:37PM
601: Finite Emulation Theory 1/perfect?  8/22/15  1:17AM
602: Removing Deep Pathology 2  8/23/15  6:35PM
603: Removing Deep Pathology 3  8/25/15  10:24AM
604: Finite Emulation Theory 2  8/26/15  2:54PM
605: Integer and Real Functions  8/27/15  1:50PM
606: Simple Theory of Types  8/29/15  6:30PM
607: Hindman's Theorem  8/30/15  3:58PM
608: Integer and Real Functions 2  9/1/15  6:40AM
609. Finite Continuation Theory 17  9/315  1:17PM
610: Function Continuation Theory 1  9/4/15  3:40PM
611: Function Emulation/Continuation Theory 2  9/8/15  12:58AM
612: Binary Operation Emulation and Continuation 1  9/7/15  4:35PM
613: Optimal Function Theory 1  9/13/15  11:30AM
614: Adventures in Formalization 1  9/14/15  1:43PM
615: Adventures in Formalization 2  9/14/15  1:44PM
616: Adventures in Formalization 3  9/14/15  1:45PM
617: Removing Connectives 1  9/115/15  7:47AM
618: Adventures in Formalization 4  9/15/15  3:07PM
619: Nonstandardism 1  9/17/15  9:57AM
620: Nonstandardism 2  9/18/15  2:12AM
621: Adventures in Formalization  5  9/18/15  12:54PM
622: Adventures in Formalization 6  9/29/15  3:33AM
623: Optimal Function Theory 2  9/22/15  12:02AM
624: Optimal Function Theory 3  9/22/15  11:18AM
625: Optimal Function Theory 4  9/23/15  10:16PM
626: Optimal Function Theory 5  9/2515  10:26PM
627: Optimal Function Theory 6  9/29/15  2:21AM
628: Optimal Function Theory 7  10/2/15  6:23PM
629: Boolean Algebra/Simplicity  10/3/15  9:41AM
630: Optimal Function Theory 8  10/3/15  6PM
631: Order Theoretic Optimization 1  10/1215  12:16AM
632: Rigorous Formalization of Mathematics 1  10/13/15  8:12PM
633: Constrained Function Theory 1  10/18/15 1AM
634: Fixed Point Minimization 1  10/20/15  11:47PM
635: Fixed Point Minimization 2  10/21/15  11:52PM
636: Fixed Point Minimization 3  10/22/15  5:49PM
637: Progress in Pi01 Incompleteness 1  10/25/15  8:45PM
638: Rigorous Formalization of Mathematics 2  10/25/15 10:47PM
639: Progress in Pi01 Incompleteness 2  10/27/15  10:38PM
640: Progress in Pi01 Incompleteness 3  10/30/15  2:30PM
641: Progress in Pi01 Incompleteness 4  10/31/15  8:12PM
642: Rigorous Formalization of Mathematics 3
643: Constrained Subsets of N, #1  11/3/15  11:57PM
644: Fixed Point Selectors 1  11/16/15  8:38AM
645: Fixed Point Minimizers #1  11/22/15  7:46PM
646: Philosophy of Incompleteness 1  Nov 24 17:19:46 EST 2015
647: General Incompleteness almost everywhere 1  11/30/15  6:52PM
648: Necessary Irrelevance 1  12/21/15  4:01AM
649: Necessary Irrelevance 2  12/21/15  8:53PM
650: Necessary Irrelevance 3  12/24/15  2:42AM
651: Pi01 Incompleteness Update  2/2/16  7:58AM
652: Pi01 Incompleteness Update/2  2/7/16  10:06PM
653: Pi01 Incompleteness/SRP,HUGE  2/8/16  3:20PM
654: Theory Inspired by Automated Proving 1  2/11/16  2:55AM
655: Pi01 Incompleteness/SRP,HUGE/2  2/12/16  11:40PM
656: Pi01 Incompleteness/SRP,HUGE/3  2/13/16  1:21PM
657: Definitional Complexity Theory 1  2/15/16  12:39AM

Harvey Friedman
```