A tribute to Rani Siromoney
1929--2019
One of the most inspiring researchers in formal language theory from India passed away recently, on September 28, 2019. Rani Siromoney, a mathematician and theoretical computer scientist, built up a life-long body of work on the mathematical study of languages and grammars that underlies the way computers work.
Working from Madras Christian College, Tambaram, she built up a strong group of students working in this area, placing Chennai early on the world map of computer science long before India became known as a centre for Information Technology.
Born on July 4, 1929, in Nazareth, Tamil Nadu, Rani Siromoney studied in Madras Christian College and became a teacher there too, getting her PhD in 1969. (In between she was a teacher at Lady Doak College, Madurai, for a year.)
Her first paper was on "Grammar of Dravidian Number Names", published in "Foundations of Language". This was when she was doing her PhD work, under the guidance of her husband Dr Gift Siromoney, a statistician and another inspiring scholar from Madras Christian College. He applied statistical methods to a wide variety of themes from his everyday life, such as Karnatic music, Tamil poetry, Meteorology, distribution of trees on campus and Linguistics. He designed the first Tamil teleprinter keyboard based on statistical principles.
Working with such an inspiring figure, Rani Siromoney entered the newly emerging field of Automata Theory. This is an exciting branch of computer science which is the study of abstract machines and automata.  The approach is to find out what kind of computational problems can be solved using such abstract machines. It combines ideas in mathematics with problems in computing. She quickly made a name for herself in this field.
Until Gift Siromoney's untimely death in 1988, the couple collaborated on a range of topics in formal languages and automata theory, including the analysis of *kolams* by mathematical means.
She was always willing to learn new areas, new techniques and seek new applications. When she was in her 60's she embarked on the study of cryptography. This is the study of designing secure communications so that third-party outsiders cannot intercept and read your message. It is a very important aspect of modern computer communications. For example, how can you ensure that your e-mail or whatsapp message is not being read by someone else? The message is encrypted so that only the genuine receiver can decode and read it.
Rani Siromoney designed perhaps the first cryptosystem for the Tamil language. She also linked cryptology which is the study of codes, with formal language theory which studies how humans learn langauge.
Over the last half-century, Rani Siromoney contributed to many sub-areas of formal language theory: the study of grammars, L-Systems, Thue systems, picture languages, languages of infinite words, puzzle grammars, and so on.
In her 70's, she worked on a wide range of problems relating to the newly emerging area of DNA computing. Here, instead of relying on normal machines (like the one I am typing this article on), DNA computing uses "living" DNA from cells, and knowledge of biochemistry, and molecular biology hardware for mathematical computations. She also related membranes and biomolecules to formal language theory. 
In 2017, when she was 88 years old, she published two papers in an area called contextual array grammars, both part of an international collaboration (with two European researchers and one of her former students). This attests to her indomitable spirit and commitment to research.
Rani Siromoney was an Editor of the prestigious journal "Theoretical Computer Science" and achieved international recognition in many professional ways. But perhaps her best achievement lies in inspiring a generation of researchers, in refusing to accept any limitations imposed by her surroundings.