def cross_over(fast_prices, slow_prices, shift=1):
    """True if fast cross over slow"""
    last_index = len(slow_prices) - 1 - shift
    previous_index = last_index - 1
    if fast_prices[last_index] > slow_prices[last_index] and fast_prices[previous_index] < slow_prices[previous_index]:
        return True
    return False