PreprintCC BY 4.0arXiv
The Undecidability of FO3 and the Calculus of Relations with Just One Binary Relation
Abstract
The validity problem for first-order logic is a well-known undecidable problem. The undecidability also holds even for FO3 and (equational formulas of) the calculus of relations. In this paper we tighten these undecidability results to the following: (1) FO3 with just one binary relation is undecidable even without equality; and (2) the calculus of relations with just one character and with only composition, union, and complement is undecidable. Additionally we prove that the finite validity problem is also undecidable for the above two classes.
Versions
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BibTeX
@misc{nakamura2026undecidability,
title = {{The Undecidability of FO3 and the Calculus of Relations with Just One Binary Relation}},
author = {Yoshiki Nakamura},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35770},
eprint = {2610.35770},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35770},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Undecidability of FO3 and the Calculus of Relations with Just One Binary Relation
AU - Yoshiki Nakamura
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.35770
UR - https://arxiv.org/abs/2610.35770
AB - The validity problem for first-order logic is a well-known undecidable problem. The undecidability also holds even for FO3 and (equational formulas of) the calculus of relations. In this paper we tighten these undecidability results to the following: (1) FO3 with just one binary relation is undecidable even without equality; and (2) the calculus of relations with just one character and with only composition, union, and complement is undecidable. Additionally we prove that the finite validity problem is also undecidable for the above two classes.
ER -