Proof of `Local definability bounds the width`
groundedproofs/Lax185574Proofs/DefinableToTypes.lean · lax-185574
What this proof establishes
Assuming the claims on the left, the claim on the right holds — checked by the archive's pipeline. Proof code is not displayed here.
In the paper
- page 17 of this submission's paper
Description
Let be the rank of for -tuples, rank and arity 2, and let and be the exponent and factor of for -tuples and rank . Fix a step and a vertex , and let and be the balls of radius and around in the next partial graph. A step keeps resolved pairs, so the radius- ball in the current partial graph of a tuple from lies in . By , the type of such a tuple is determined by its type of rank in the induced partial graph on . This partial graph is definable in an expansion of the graph by predicates with at most parameters, so the type over the parameters of rank determines the latter. bounds the number of these types by .
The argument is carried out for the graph classes of the archive and their monadic dependence, and transferred to the graph classes used here.