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Jack Ma, chairman of Alibaba, again warned that Bitcoin is a bubble (https://www.bloomberg.com/news/articles/2018-06-25/jack-ma-embraces-blockchain-for-ant-but-warns-of-bitcoin-bubble).
However, one must not forget that Bitcoin is by far the most widely used public blockchain alongside with Ethereum - It is difficult if not impossible to have a clear cut between public blockchains and cryptocurrencies in such an infant industry.