arXiv subjects

Miodrag Živković

Publications and source records attributed to Miodrag Živković.

4 recordsLinked to original sources

arXiv2019

Fully Automatic, Verified Classification of all Frankl-Complete (FC(6)) Set Families

The Frankl's conjecture, formulated in 1979. and still open, states that in every family of sets closed for unions there is an element contained in at least half of the sets. A family Fc is called Frankl-complete (or FC-family) if in every union-closed family F containing Fc, one of the elements of union Fc occurs in at least half of the elements of F (so F satisfies the Frankl's condition). FC-families play an important role in attacking the Frankl's conjecture, since they enable significant search space pruning. We extend previous work by giving a total characterization of all FC-families over a 6-element universe, by defining and enumerating all minimal FC and maximal nonFC-families. We use a fully automated, computer assisted approach, formally verified within the proof-assistant Isabelle/HOL.

cs.LO↗

arXiv2016

On the number of equivalence classes of invertible Boolean functions under action of permutation of variables on domain and range

Let $V_n$ be the number of equivalence classes of invertible maps from $\{0,1\}^n$ to $\{0,1\}^n$, under action of permutation of variables on domain and range. So far, the values $V_n$ have been known for $n\le 6$. This paper describes the procedure by which the values of $V_n$ are calculated for $n\le 30$.

math.CO↗

arXiv2012

Formalizing Frankl's Conjecture: FC-families

The Frankl's conjecture, formulated in 1979. and still open, states that in every family of sets closed for unions there is an element contained in at least half of the sets. FC-families are families for which it is proved that every union-closed family containing them satisfies the Frankl's condition (e.g., in every union-closed family that contains a one-element set {a}, the element a is contained in at least half of the sets, so families of the form {a} are the simplest FC-families). FC-families play an important role in attacking the Frankl's conjecture, since they enable significant search space pruning. We present a formalization of the computer assisted approach for proving that a family is an FC-family. Proof-by-computation paradigm is used and the proof assistant Isabelle/HOL is used both to check mathematical content, and to perform (verified) combinatorial searches on which the proofs rely. FC-families known in the literature are confirmed, and a new FC-family is discovered.

cs.DM↗

arXiv2005

Classification of small $(0,1)$ matrices

Denote by $A_n$ the set of square $(0,1)$ matrices of order $n$. The set $A_n$, $n\le8$, is partitioned into row/column permutation equivalence classes enabling derivation of various facts by simple counting. For example, the number of regular $(0,1)$ matrices of order 8 is 10160459763342013440. Let $D_n$, $S_n$ denote the set of absolute determinant values and Smith normal forms of matrices from $A_n$. Denote by $a_n$ the smallest integer not in $D_n$. The sets $\mathcal{D}_9$ and $\mathcal{S}_9$ are obtained; especially, $a_9=103$. The lower bounds for $a_n$, $10\le n\le 19$, (exceeding the known lower bound $a_n\ge 2f_{n-1}$, where $f_n$ is $n$th Fibonacci number) are obtained. Row/permutation equivalence classes of $A_n$ correspond to bipartite graphs with $n$ black and $n$ white vertices, and so the other applications of the classification are possible.

math.CO↗