gpu_cache = ["cache-a", "cache-b"]
cpu_cache = []

# Cache C needs GPU space, so cache A moves to CPU memory.
cpu_cache.append(gpu_cache.pop(0))
gpu_cache.append("cache-c")

print("GPU after cache C arrives:", gpu_cache)
print("CPU after cache C arrives:", cpu_cache)

# Cache A is needed again, so it returns to the GPU.
cpu_cache.remove("cache-a")
cpu_cache.append(gpu_cache.pop(0))
gpu_cache.append("cache-a")

print("GPU after cache A returns:", gpu_cache)
print("CPU after cache A returns:", cpu_cache)

# Output:
"""
GPU after cache C arrives: ['cache-b', 'cache-c']
CPU after cache C arrives: ['cache-a']
GPU after cache A returns: ['cache-c', 'cache-a']
CPU after cache A returns: ['cache-b']
"""