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Pilz's Extended 1-2-3 Conjecture


Pilz's extended 1-2-3 conjecture asserts that, for every nonempty finite set A of positive integers and every positive integer n,

 |S_n(A)|>=n,
(1)

where S_n(A)=ADelta2ADelta...DeltanA, jA={ja:a in A}, and Delta denotes symmetric difference. Equivalently, at least n integers have an odd number of ordered representations ab with a in A and 1<=b<=n. The bound is sharp, since A={a} gives exactly n elements. The 1-2-3 conjecture restricts A to an initial interval of positive integers (Huang et al. 2010). Holdridge and Pach (2026) proved the extended conjecture for all sufficiently large n.

The anonymously authored manuscript Pilz's Extended 1-2-3 Conjecture over Every Field (2026a) reports a proof for every n in a stronger weighted form. For each prime p, introduce an indeterminate x_p and set X(a)=product_(p)x_p^(v_p(a)), where v_p(a) is the exponent of p in the prime factorization of a. For any field K and nonzero coefficients c_1, c_2, ..., c_n in K, define

 P_(n,c)=sum_(a=1)^nc_aX(a).
(2)

Every nonzero polynomial or Laurent polynomial multiple of P_(n,c) is reported to have at least n nonzero monomials. Taking K to be the two-element finite field and all c_a=1 gives the set-theoretic conjecture. The interval hypothesis matters: over that field, (1+x+x^2)(1+x)=1+x^3, so replacing {1,...,n} by an arbitrary n-element set of positive integer indices does not preserve the bound.

Equivalently, the weighted multiplicative convolution

 (T_cf)(m)=sum_(1<=a<=n; a|m)c_af(m/a)
(3)

has at least n nonzero values for every nonzero K-valued function f on the positive integers with finite support. For values in a vector space, the reported bound is n+rho-1, where rho is the dimension of the vector space span of the input values. For values in a nonzero unital module over a commutative ring, the bound n holds for every nonzero finitely supported input iff multiplication by each c_a is injective. For commuting endomorphisms of an additive commutative monoid, the corresponding criterion is that each map sends only zero to zero. The manuscript also reports uniqueness of recovery from t corrupted and s erased output coordinates when 2t+s<n. This is a uniqueness statement rather than an efficient decoding algorithm.

At a prime index l>=3, the reported equality classification is

 |S_l(A)|=l<==>F_A=X(b)P_(l,1)^(2^e-1)
(4)

for some integers b>=1 and e>=0, where F_A=sum_(a in A)X(a) is taken over the two-element finite field. The corresponding output is S_l(A)={ba^(2^e):1<=a<=l}. For odd n and even |A|, the parity identity |S_n(A)|=n|A|  (mod2) sharpens the bound to n+1, attained by A={1,2}.

For fixed A, the limiting density

 h(A)=lim_(n->infty)(|S_n(A)|)/n=sum_(emptyset!=J subset= A)(-2)^(|J|-1)(minJ)/(lcm(J))
(5)

exists and is a rational number (Ke and Meyer 2025, Holdridge and Pach 2026). The anonymous companion The Optimal 4/3 Density Bound in Pilz's Problem (2026b) reports h(A)>=4/3 unless A={a} or A={a,2a}, which have density one. The constant is sharp at A={1,3}. After division by the greatest common divisor, nonexceptional sets consisting of powers of two satisfy the stronger bound h(A)>=3/2. This is an asymptotic statement with A fixed, not a bound |S_n(A)|>=4n/3 for every n. For example, S_3({1,2,3})={1,4,9}.

The project attributes mathematical arguments and Lean formalization to substantial AI assistance. It supplies public Lean 4 developments and reports independent kernel replay of the weighted proof. The authors state that the written proofs have not been checked line by line by a human mathematician. The density formalization is independent of the finite-interval theorem.


See also

Convolution, Polynomial, Symmetric Difference

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References

--. "Pilz's Extended 1-2-3 Conjecture over Every Field: Sparse Multiples of Weighted Integer Intervals." Oct. 23, 2026a. https://github.com/odd-products/extended-1-2-3-conjecture-of-Pilz/blob/b6ab2c22c0ba3658ef912e9db41ae91c7c8977f3/pilz-weighted/paper/main.pdf. Formal sources: https://doi.org/10.5281/zenodo.23568997.--. "The Optimal 4/3 Density Bound in Pilz's Problem." 2026b. https://github.com/odd-products/extended-1-2-3-conjecture-of-Pilz/blob/b6ab2c22c0ba3658ef912e9db41ae91c7c8977f3/pilz-density/paper/main.pdf.Holdridge, P. and Pach, P. P. "On the Extended 1-2-3 Conjecture of Pilz." 1 Jul 2026. https://arxiv.org/abs/2607.00934v1.Huang, P.-Y.; Ke, W.-F.; and Pilz, G. F. "The Cardinality of Some Symmetric Differences." Proc. Amer. Math. Soc. 138, 787-797, 2010. https://doi.org/10.1090/S0002-9939-09-10189-2.Ke, W.-F. and Meyer, J. H. "On a Conjecture Regarding the Symmetric Difference of Certain Sets." Bull. Austral. Math. Soc. 111, 397-404, 2025. https://doi.org/10.1017/S0004972724000807.

Cite this as:

Weisstein, Eric W. "Pilz's Extended 1-2-3 Conjecture." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/PilzsExtended1-2-3Conjecture.html

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