Read this: Symbiosis (from Greek σύν "together" and βίωσις "living") is close and often long-term interaction between two different biological species. In 1877 Albert Bernhard Frank used the word symbiosis (which previously had been used to depict people living together in community) to describe the mutualistic relationship in lichens. In 1879, the German mycologist Heinrich Anton de Bary defined it as "the living together of unlike organisms."

What year did Albert Bernhard Frank agree to define "symbiosis" as "the living together of unlike organisms."?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable