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.

Read the Lean proof on GitHub

In the paper

  • page 17 of this submission's paper

Description

Let q′q' be the rank of LocalToGlobalLocalToGlobal for qq-tuples, rank qq and arity 2, and let aa and FF be the exponent and factor of TypeBoundTypeBound for qq-tuples and rank q′+q0q' + q₀. Fix a step tt and a vertex vv, and let BB and WW be the balls of radius rr and r+7qr + 7^q around vv in the next partial graph. A step keeps resolved pairs, so the radius-7q7^q ball in the current partial graph of a tuple from BB lies in WW. By LocalToGlobalLocalToGlobal, the type of such a tuple is determined by its type of rank q′q' in the induced partial graph on WW. This partial graph is definable in an expansion of the graph by cc predicates with at most ss parameters, so the type over the parameters of rank q′+q0q' + q₀ determines the latter. TypeBoundTypeBound bounds the number of these types by F⋅(s+1)aF · (s + 1)^a.

The argument is carried out for the graph classes of the archive and their monadic dependence, and transferred to the graph classes used here.