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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def raster(times, indices, max_time=None, max_index=None, x_label="Timestep", y_label="Index", **kwargs):
 """Plots a raster plot given times and indices of events."""

    # set default size to 1
    if 's' not in kwargs:
        kwargs['s'] = 1
    scatter(times, indices, **kwargs)
    
    if max_time is None:
        max_time = max(times)
    if max_index is None:
        max_index = max(indices)
    axis((0, max_time, 0, max_index))
    if x_label is not None: xlabel(x_label)
    if y_label is not None: ylabel(y_label)