A Logspace Constructive Proof of L=SL

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Main Authors: Buss, Sam, Dhayal, Anant, Kabanets, Valentine, Kolokolova, Antonina, Mouli, Sasank
Format: Preprint
Published: 2025
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_version_ 1866917081335726080
author Buss, Sam
Dhayal, Anant
Kabanets, Valentine
Kolokolova, Antonina
Mouli, Sasank
author_facet Buss, Sam
Dhayal, Anant
Kabanets, Valentine
Kolokolova, Antonina
Mouli, Sasank
contents We formalize the proof of Reingold's Theorem that SL=L [Rei05] in the theory of bounded arithmetic VL, which corresponds to ``logspace reasoning''. As a consequence, we get that VL=VSL, where VSL is the theory of bounded arithmetic for ``symmetric-logspace reasoning''. This resolves in the affirmative an old open question from Kolokolova [Kol05] (see also Cook-Nguyen [NC10]). Our proof relies on the Rozenman-Vadhan alternative proof of Reingold's Theorem ([RV05]). To formalize this proof in VL, we need to avoid reasoning about eigenvalues and eigenvectors (common in both original proofs of SL=L). We achieve this by using some results from Buss-Kabanets-Kolokolova-Koucký [Bus+20] that allow VL to reason about graph expansion in combinatorial terms.
format Preprint
id arxiv_https___arxiv_org_abs_2511_12011
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle A Logspace Constructive Proof of L=SL
Buss, Sam
Dhayal, Anant
Kabanets, Valentine
Kolokolova, Antonina
Mouli, Sasank
Logic in Computer Science
Logic
03D15, 03F30, 03F35, 68Q15, 68Q10
F.4.1; F.1.1
We formalize the proof of Reingold's Theorem that SL=L [Rei05] in the theory of bounded arithmetic VL, which corresponds to ``logspace reasoning''. As a consequence, we get that VL=VSL, where VSL is the theory of bounded arithmetic for ``symmetric-logspace reasoning''. This resolves in the affirmative an old open question from Kolokolova [Kol05] (see also Cook-Nguyen [NC10]). Our proof relies on the Rozenman-Vadhan alternative proof of Reingold's Theorem ([RV05]). To formalize this proof in VL, we need to avoid reasoning about eigenvalues and eigenvectors (common in both original proofs of SL=L). We achieve this by using some results from Buss-Kabanets-Kolokolova-Koucký [Bus+20] that allow VL to reason about graph expansion in combinatorial terms.
title A Logspace Constructive Proof of L=SL
topic Logic in Computer Science
Logic
03D15, 03F30, 03F35, 68Q15, 68Q10
F.4.1; F.1.1
url https://arxiv.org/abs/2511.12011