He is an expert in semiotics, and his theories are very profound.

What does this masu symbol mean?

This text is organized using section signs.

What does this at sign mean?

He understands the importance of learning.

He is majoring in psychology.

Gaku is my best friend.

He has a deep interest in archaeology.

He is good at geometry.

Differential geometry is a field of mathematics that studies geometric objects such as curves and surfaces using differential and integral calculus.