[6, 2802] finitely based
[6, 2802] is a commutative semigroup with 2 idempotents and a zero, 1. It is finitely based: 2 identities define its variety, which 2 other semigroups of order six also generate.
Cayley table
| · | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 2 | 1 | 1 | 1 | 1 | 3 | 1 |
| 3 | 1 | 1 | 1 | 1 | 1 | 1 |
| 4 | 1 | 1 | 1 | 1 | 1 | 4 |
| 5 | 1 | 3 | 1 | 1 | 2 | 1 |
| 6 | 1 | 1 | 1 | 4 | 1 | 6 |
The product of the row element and the column element, numbered as in Smallsemi. Blue: idempotents on the diagonal; grey: the zero.
Structure
- Smallsemi
- SmallSemigroup(6, 2802)
- Idempotents
- 1, 6
- Zero
- 1
- Identity
- none
- Nilpotent
- no
- Commutative
- yes
- Regular
- no
- Group
- no
- 𝒥-classes
- 6
- Rank
- 3, generated by {4, 5, 6}
- Self-dual
- yes: anti-isomorphic to itself
Identity basis
Shortest known basis: 2 identities irredundant
- xy ≈ yx
- x³yz ≈ x²yz
Irredundant: none of these identities follows from the others; for each, a semigroup satisfies the others but not it. Obtained from a basis certified in Lean by removing identities that follow from the others, with the prover Vampire; the equivalence rests on Vampire's proofs, not on Lean. Shortest known, not known to be minimal.
Basis certified in Lean: 5 identities
- x⁴ ≈ x⁵
- xy ≈ yx
- x⁴y ≈ x³y
- x³y² ≈ x²y²
- x³yz ≈ x²yz
Lean proof
Endpoint theorem: SemigroupBasis.CoRoots.Order6GenericCASSubdirectS6_2802.basisFor
BasisFor SemigroupBasis.CoRoots.Order6GenericCASSubdirectS6_2802.rootSemigroup✝ SemigroupBasis.CoRoots.Order6GenericCASSubdirectS6_2802.rootBasis✝
- Table
- The theorem is about the semigroup with exactly this table.
- Method
- family proof. One basis is proved once to derive every identity of every semigroup of a family; on each table only the identities of the basis are checked, by computation.
- Size
- Checking this class alone compiles 27 Lean files with 8,232 lines: the endpoint theorem and everything it imports, the shared library included. All of it is shared with the proofs of other classes.
- Census
- SemiBase.Census.S6_2802 checks that the theorem is about the table of this class and concludes Classified; SemiBase.Catalogue.Order6.S6_2802 is the table, with the elements numbered 0 to 5.
Variety
[6, 2802] generates the variety V[2802]; 2 other semigroups of order six generate it too, and 942 semigroups of order six lie in it. [6, 2802] lies in 8 of the 505 varieties of the census, those whose basis it satisfies.
- Directly above
- Directly below
V[2802] in the inclusion graph, with the varieties above and below it.
Generating the same variety
Nearby tables
Semigroups whose Smallsemi table differs from this one in one or two entries (row, column), as the tables are listed, not up to renumbering.