He is an expert in topology.

He is an expert in crystallography.

Semiotics is the study of signs and symbols used in society and culture.

He is an expert in psychiatry.

This reaction has reached chemical equilibrium.

He is an expert in oenology and has a deep knowledge of wines from around the world.

He is majoring in history at university.

He is a world-famous scientist.

He is majoring in ethics at university.

I go to the local orchestra concert every weekend.