At the moment I am reading the book Ramanujan's Papers by B.J. Venkatachala, V. Vinay and C.S. Yogananda; when clarifying some doubt with a professor, he told me that Srinivasa Ramanujan used Galois theory in many places of his work without actually knowing them by any means but he knew the theory just by his intuition.
I was amazed.
I asked the professor what areas in mathematics are known to be known by Srinivasa Ramanujan, like Galois theory. He gave me a broad answer that Srinivasa Ramanujan is a genius in analytic number theory.
I am interested in knowing some theories in mathematics which were used by Srinivasa Ramanujan without him knowing their name (as in Galois theory), but understanding them by intuition, where people later understood that this is the theory Srinivasa Ramanujan used.
I think there will be many such theories in mathematics. Can anybody tell me any of your such observations in his work?
Thanks in advance.