[L₂,L₋₂] = 4·L₀ + c/2 (exact; at c=1: 4L₀ + 1/2)

Closed-form evaluation of the Virasoro central term at m = 2. [L_m, L_{−m}] = 2m·L_0 + (c/12)·(m³−m); substituting m = 2 gives 4·L_0 + (c/12)·6 = 4·L_0 + c/2 (canonical sympy string "4*L0 + c/2"). At m = 1 the central term vanishes:…