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Loogle Search - Mathlib Type Signature Search

loogle-search

Search Mathlib for lemmas by type signature pattern

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Full skill instructions

Loogle Search - Mathlib Type Signature Search

Search Mathlib for lemmas by type signature pattern.

When to Use

  • Finding a lemma when you know the type shape but not the name
  • Discovering what's available for a type (e.g., all Nontrivial ↔ _ lemmas)
  • Type-directed proof search

Commands

# Search by pattern (uses server if running, else direct)
loogle-search "Nontrivial _ ↔ _"
loogle-search "(?a → ?b) → List ?a → List ?b"
loogle-search "IsCyclic, center"

# JSON output
loogle-search "List.map" --json

# Start server for fast queries (keeps index in memory)
loogle-server &

Query Syntax

PatternMeaning
_Any single type
?a, ?bType variables (same variable = same type)
Foo, BarMust mention both Foo and Bar
Foo.barExact name match

Examples

# Find lemmas relating Nontrivial and cardinality
loogle-search "Nontrivial _ ↔ _ < Fintype.card _"

# Find map-like functions
loogle-search "(?a → ?b) → List ?a → List ?b"
# → List.map, List.pmap, ...

# Find everything about cyclic groups and center
loogle-search "IsCyclic, center"
# → commutative_of_cyclic_center_quotient, ...

# Find Fintype.card lemmas
loogle-search "Fintype.card"

Performance

  • With server running: ~100-200ms per query
  • Cold start (no server): ~10s per query (loads 343MB index)

Setup

Loogle must be built first:

cd ~/​tools/​loogle && lake build
lake build LoogleMathlibCache  # or use --write-index

Integration with Proofs

When stuck in a Lean proof:

  1. Identify what type shape you need
  2. Query Loogle to find the lemma name
  3. Apply the lemma in your proof
-- Goal: Nontrivial G from 1 < Fintype.card G
-- Query: loogle-search "Nontrivial _ ↔ 1 < Fintype.card _"
-- Found: Fintype.one_lt_card_iff_nontrivial
exact Fintype.one_lt_card_iff_nontrivial.mpr h

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