Provided is a high-repetition-rate femtosecond regenerative amplification system. In one embodiment, the structure includes a retardation layer, a first polarizing layer, a first uniaxial optical compensation layer, a second polarizing layer and a second uniaxial optical compensation layer. If two chords c and d among the series of chords a, b, c, d, e, f are changed into different ones, according to the users preference or to make them more appropriate to the motif melody, the chord b adjacent to the changed c is automatically corrected into b* so that both chord connections from a to b* and from b* to the changed c can be more musically natural. The synthetic resin film side also has an extension from the lower fold which is folded upwardly to join with and enclose a lower portion of the mesh side wall. A first risk dimension is precalculated for the case of continued deceleration and a second risk dimension is precalculated for the case of unbraked further movement of the vehicle.