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Groups: LMFDB finite-group label (small-group identification) #61

Description

@CBirkbeck

Goal

Provide the LMFDB group label N.i — order N and the GAP small-group id i — i.e. a canonical identification of a finite group up to isomorphism.

What already exists

  • mathlib: finite group theory, Fintype.card, isomorphism (MulEquiv), and named small groups (DihedralGroup, QuaternionGroup, CyclicGroup/ZMod, Equiv.Perm/alternatingGroup). There is no small-groups catalogue / canonical labelling.

What's missing

  • A decidable up-to-isomorphism identifier for small finite groups matching the GAP/LMFDB N.i numbering (at least for small N), or a mapping from mathlib's named families to their labels.

Test cases

  • C_2 = 2.1, C_2² = 4.2, S_3 = 6.1, Q_8 = 8.4, D_4 = 8.3.

LMFDB targets

New area, not yet in the Verso blueprint — links go to the LMFDB knowls.

Activity

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    groupsFinite / abstract group invariantslevel: intermediateSome mathlib/Lean experience helpfulpriority: lowLower priority — newer/beta LMFDB section, secondary to the core MF/EC/NF focus

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