Filter Equivariant Functions: A symmetric account of length-general extrapolation on lists

Fuente: arXiv
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Autores principales: Lewis, Owen, Ghani, Neil, Dudzik, Andrew, Perivolaropoulos, Christos, Pascanu, Razvan, Veličković, Petar
Formato: Preprint
Publicado: 2025
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author Lewis, Owen
Ghani, Neil
Dudzik, Andrew
Perivolaropoulos, Christos
Pascanu, Razvan
Veličković, Petar
author_facet Lewis, Owen
Ghani, Neil
Dudzik, Andrew
Perivolaropoulos, Christos
Pascanu, Razvan
Veličković, Petar
contents What should a function that extrapolates beyond known input/output examples look like? This is a tricky question to answer in general, as any function matching the outputs on those examples can in principle be a correct extrapolant. We argue that a "good" extrapolant should follow certain kinds of rules, and here we study a particularly appealing criterion for rule-following in list functions: that the function should behave predictably even when certain elements are removed. In functional programming, a standard way to express such removal operations is by using a filter function. Accordingly, our paper introduces a new semantic class of functions -- the filter equivariant functions. We show that this class contains interesting examples, prove some basic theorems about it, and relate it to the well-known class of map equivariant functions. We also present a geometric account of filter equivariants, showing how they correspond naturally to certain simplicial structures. Our highlight result is the amalgamation algorithm, which constructs any filter-equivariant function's output by first studying how it behaves on sublists of the input, in a way that extrapolates perfectly.
format Preprint
id arxiv_https___arxiv_org_abs_2507_08796
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Filter Equivariant Functions: A symmetric account of length-general extrapolation on lists
Lewis, Owen
Ghani, Neil
Dudzik, Andrew
Perivolaropoulos, Christos
Pascanu, Razvan
Veličković, Petar
Programming Languages
Machine Learning
What should a function that extrapolates beyond known input/output examples look like? This is a tricky question to answer in general, as any function matching the outputs on those examples can in principle be a correct extrapolant. We argue that a "good" extrapolant should follow certain kinds of rules, and here we study a particularly appealing criterion for rule-following in list functions: that the function should behave predictably even when certain elements are removed. In functional programming, a standard way to express such removal operations is by using a filter function. Accordingly, our paper introduces a new semantic class of functions -- the filter equivariant functions. We show that this class contains interesting examples, prove some basic theorems about it, and relate it to the well-known class of map equivariant functions. We also present a geometric account of filter equivariants, showing how they correspond naturally to certain simplicial structures. Our highlight result is the amalgamation algorithm, which constructs any filter-equivariant function's output by first studying how it behaves on sublists of the input, in a way that extrapolates perfectly.
title Filter Equivariant Functions: A symmetric account of length-general extrapolation on lists
topic Programming Languages
Machine Learning
url https://arxiv.org/abs/2507.08796