Left-derived functors of the tensor product: Torₙ^R(A, B) = Hₙ(P• ⊗_R B) for a projective resolution P• → A. Measures torsion: Tor₁^ℤ(A, ℤ/n) = A[n]. Symmetric in its two arguments.
Left-derived functors of the tensor product: Torₙ^R(A, B) = Hₙ(P• ⊗_R B) for a projective resolution P• → A. Measures torsion: Tor₁^ℤ(A, ℤ/n) = A[n]. Symmetric in its two arguments.