We investigate the light-cone quantization of phi(3)-theory in (1 + 1)
dimensions with a regularization of the discretized light-cone moment
um k(+). Solving a second-class constraint associated with the k(+)=0
mode, we show that the k(+)=0 mode propagates along the internal lines
of Feynman diagrams in any order of perturbation, hence our theory re
covers Lorentz invariance.