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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 mean(attrs, inputs, proto_obj):
 """Mean of all the input tensors."""

    concat_input = [symbol.expand_dims(op_input, axis=0) for op_input in inputs]
    concat_sym = symbol.concat(*concat_input, dim=0)
    mean_sym = symbol.mean(concat_sym, axis=0)
    return mean_sym, attrs, inputs