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There is a nice Apache 2.0-licensed project that already implements the foundation of a way more elaborate product that I intend to sell as proprietary.
Something like the 70% of the code will be modified or rewritten, so it's not really like I'm including it as a module or library.
Unfortunately I cannot release the sources of the final product as OSS, but it is possible to add credits and acknowledgements.
Would this be legal?