Simulation tests of overlapping hard-to-soft pulses for GRBs 081224 (first row) and 100707A (second row) are taken as a template. The six panels show the Ep-evolution pattern of the simulated GRB with different pulse separations: 10 s (first column), 5 s (second column), 3 s (third column). The vertical dash lines mark the onset of the second pulses. The symbols are the same as in Figure 2.