He is known as an excellent theoretician.

He is immersed in the study of string theory.

He is particularly interested in game theory within economics.

He is writing a paper on coding theory.

String theory is a branch of physics that is a theory for understanding the basic structure of the universe.

He wrote a new paper on string theory.

He is particularly interested in string theory in physics.

He likes to take a walk in the park at dusk.

He is spending a lot of time on experimental research.

The Calopteryx cornelia is a species endemic to Japan, and it has beautiful wings.