The resonant level (Anderson) model: a single fermionic level at energy ε_d coupled symmetrically to left/right metallic leads with hybridization width Γ = π|V|²ρ. The spectral function is a Lorentzian A(ω) = Γ/π / [(ω−ε_d)²+Γ²]. Transmission at the Fermi level T(E_F) = Γ²/[E_F²+Γ²] (with ε_d shifted by gate). Zero-temperature conductance G = G₀·T(E_F) where G₀ = 2e²/h. Finite T smears the resonance via the Fermi-Dirac window function −∂f/∂ε.