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Re: Number of variables needed to axiomatize first order predicate calculus?
Posted:
Mar 15, 2013 11:25 PM


On Mar 16, 10:55 am, me <me154...@gmail.com> wrote: > On Mar 15, 1:46 am, Graham Cooper <grahamcoop...@gmail.com> wrote: > > > > > On Mar 13, 5:54 pm, George Greene <gree...@email.unc.edu> wrote: > > > > On Mar 8, 6:02 pm, Frederick Williams <freddywilli...@btinternet.com> > > > wrote: > > > > > It is well known that at least three variables are needed to axiomatize > > > > sentential calculus, by which I mean that at least three letters are > > > > needed to write down the axioms and rules. > > > > Come ON! You can't take your own question seriously until > > > and UNLESS YOU FIRST *specify* a *specification*LANGUAGE*!! > > > > The specificationlanguage you used to specify the axioms of > > > propositional calculus > > > is one that NO ONE HAS *EVER* seen used IN ANY other context! > > > It basically just copies the grammar of the underlying language AS > > > ASSUMED > > > and then INTRODUCES A CONCEPT from a COMPLETELY HIGHER ORDER, > > > namely firstorder, without ANY PRETEXT of explication! It > > > universally quantifies > > > over the things that it is trying to "specify", even though universal > > > quantification > > > is EXPLICITLY PROHIBITED in the objectlanguage and even though this > > > specification > > > language itself does NOT explicitly contain any quantifiersymbols! > > > It is EASY to > > > "get small" if you just LEAVE OUT WHOLE CHUNKS of explication of what > > > you > > > are doing! > > > > The use of ","(comma) and "/"(slash) for clarifying that from some > > > finite collection > > > of input sentences, you can infer some other finite collection of > > > output sentences, > > > IS (thank god) used elsewhere and I suppose that could be tolerated as > > > being a > > > paradigmwide linguisitic convention for the specification of logics > > > ascollections > > > ofrulesingeneral ANYway. You could certainly begin this quest by > > > saying that you > > > would like to state all the inference rules of firstorder logic using > > > this comma/slash > > > framework. > > > > But in general it is just going to be MUCH HARDER because arguably THE > > > MOST > > > important inference rule in FOL is NOT an inference rule simpliciter, > > > but RATHER > > > a METAinference rule, or, literally, a SECONDORDER*FIRSTORDER* > > > inferencerule, > > > namely, UNIVERSAL GENERALIZATION, in which you infer a sentence in FOL > > > (a universally > > > quantified sentence) NOT from some prior collection of sentences but > > > rather FROM A *PROOF*! > > > Basically, from [ B  phi(x) ], where B is a finite set of sentences > > > with x not occurring in them, > > > you infer Ax[phi(x)]. The mere DARING of this NESTING of ""  not > > > to mention, HOW MANY > > > VARIABLES does it take TO EVEN STATE the nonoccurrence clause??  > > > the rule could > > > basically be written [ B  phi(x) ]  Ax[phi(x)]  oh, and HOW > > > MANY VARIABLES does it > > > take to explain what x *as*parameter*of*phi(.)* means, as OPPOSED to > > > what variables > > > mean in other contexts  remember, in your propositional/0thorder > > > treatment, variables > > > ONLY meant PROPOSITIONS  is certainly BEYOND the pale of ANY > > > specification language that you might have been trying to use FOR ANY > > > OTHER purpose! > > > If the language in which you are doing this is not CONSTANT (or at > > > least constant in > > > paradigm or parametric profile) across the various languages&levelsof > > > logics that > > > you are investigating, then "the number of variables it takes" is just > > > not going to be > > > meaningful as a metric. Oh, yeah, and then you also have to ask how > > > many variables > > > it takes to explain what kind of thing "phi(.)" is. Phi(.) is after > > > all ITSELF a universally > > > quantified VARIABLE. > > > Eventually you should arrive at a nOL logic with syntax complex > > enough to encapsulate nOL. > > > But 2OL needn't be MORE complex SYNTAX, just fewer restrictions. > > > e.g. lowercase = terms, uppercase = variables > > > 1OL > > add( M, 0, M ) > > add( M, s(N), (S) ) < add( M, N, S ). > > > 2OL > > P(s(0)) < ( P(X) > P(s(X) ) & P(0) ) > > > this is HIGH ORDER PROLOG where predicates may be VARIABLES and match > > to generic prolog clauses. e.g. P could match with notsmallest(X), > > where notsmallest(X)>notsmallest(X+1) > > >  > > > Now all the AXIOMS of the theory may be written in a SUBSET of the > > full 1OL. > > > e.g. HORN CLAUSES using only > > > p1(...) & p2(...) & p3(...) > pa(...) > > >  > > > What you want to look for is a SUBSET of the (1OL) language that can > > perform some computational feat  e.g. be Turing Machine Equivalent. > > > Horn Clauses have this property since > > > UNIFY( f(a,b,c...) , f2(z,y,x,...) ) > > > which finds a COMMON predicate between 2 > > is Turing Equivalent. > > > Then this computation method must be utilised to EXPAND on the limited > > 2OL syntax. > > >  > > > The way I do this is using Naive Set Definition to specify which > > variable in each predicate a SET is referencing. > > > e( A, evens ) : even(A). > > > *this example is simple, even() only has one argument. > > > Then I can process ALL() quantifiers via Set References, rather than > > explicitly stating which term to Quantify over in Quantified Logic > > style.. A(x), p(...x...) >=... > > which is rather messy with partial formula insides hanging out like > > that!. > > >  > > > So yes you can INCREASE the complexity of 2OL syntax, but it's going > > to get convoluted with string processing and looking inside predicate > > types, or you can use a subset of 1OL syntax to write the axioms which > > work on a simpler processing system which can still do the computing > > work necessary. > > > e.g. Not All Numbers Are Evens > > > ~A(X) e( X, evens ) > > > I bypass referencing internals by using Set Referencing > > > !(ss( nats, evens )) > > > Not all members of nats are members of evens. > > >  > > > which is in Horn Clause format same as 2OL axioms and computable! > > > !(ss( S1, S2 ) < intersect( S1, !(S2)). > > > A 2OL Axiom. > > > (which will return the 1st ODD when invoked) > > > Herc > > > www.BLoCKPROLOG.com > > Oix >
IOW, its quite possible to embed a more complicated grammar in a simpler grammar!
Then you can use a computer to evaluate the language..
LOGIC SYSTEM (wff  10L)  HORN CLAUSE (reverse inference rules  2OL) ====================== 3GL INTERPRETER (+ Database) ________________________ COMPUTER
Then you can merely TRANSLATE the wff to any Logic Language you like.
INPUT> ALL(N):EVENS N e NATS ? V <PREPARSER> V PROLOG> ss( EVENS, NATS) PROLOG> e(@A, EVENS) , e(A, NATS) PROLOG> YES V <POST_PARSER> V RESULT> ALL(N):EVENS N e NATS
Parsing into QUANTIFIER LINGO is not required for problem solving though.
Herc  www.BLoCKPROLOG.com



