pub fn tensor_from_table(t: &CharacterTable) -> Option<Vec<Vec<Vec<u128>>>>Expand description
The tensor (Clebsch–Gordan) decomposition of the irreducibles: N[i][j][k] = ⟨χ_i·χ_j, χ_k⟩, the
multiplicity of χ_k in the tensor product χ_i ⊗ χ_j. These are the fusion coefficients — the
structure constants of the representation ring R(G) (the multiplication dual to the character table’s
addition). Computed from a character table:
N[i][j][k] = (1/|G|) Σ_r |C_r|·χ_i(C_r)·χ_j(C_r)·χ_k(C_{r̄}) over the table’s GF(p); each is a small
non-negative integer ≤ d_i·d_j ≤ |G| < p, so it decodes uniquely. FAIL-CLOSED: returns None unless
every fusion product has the right dimension (Σ_k N[i][j][k]·d_k = d_i·d_j), the trivial character is a
unit (χ_triv ⊗ χ_j = χ_j), and the coefficients are symmetric (N[i][j][k] = N[j][i][k]). Indices
align with character_table’s rows.