[leburgel]

isless on ProductSectors computes the index of every factor of both sectors, also when they are equal, which is the common case when sorting tuples of sectors. Checking isequal first makes that 2–4× cheaper; different sectors are unaffected.

isless(a, a)	before	after
FermionParity ⊠ U1Irrep ⊠ SU2Irrep ⊠ U1Irrep	10 ns	5 ns
FermionParity ⊠ U1Irrep ⊠ SU3Irrep	19–21 ns	5 ns

Reproducer

using TensorKitSectors, BenchmarkTools
a = FermionParity(1) ⊠ U1Irrep(1) ⊠ SU2Irrep(1 // 2) ⊠ U1Irrep(1)
b = FermionParity(0) ⊠ U1Irrep(-2) ⊠ SU2Irrep(1) ⊠ U1Irrep(3)
@btime isless($a, $a)
@btime isless($a, $b)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/product.jl	94.52% <100.00%> (+0.02%)	⬆️

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