Transverse fundamental kink mode in a coronal slab with a density contrast ρ_i/ρ_e = 3. The dependence on [k_y, k_z] of the phase speed $v_{\mathrm{ph}}=\omega /\sqrt{k_y^2+k_z^2}$ is shown by the equally spaced contours. Trapped modes are allowed for all [k_y ≥ 0, k_z > 0], with both body (n_i² > 0) and surface (n_i² < 0) modes being relevant. The color map represents the parameter n_i, and is restricted to body modes.