In the organic chemistry class, there was an explanation of the Natta projection.

His actions change depending on the circumstances.

He is a world-renowned ichthyologist.

The rainbow lorikeet is known for its vibrant colors.

He said, 'It's difficult to make a life,' explaining the phrase 'When a man steps over the threshold, he has seven enemies.'

He used a handkerchief to wipe his sweat.

Shingo is my best friend.

I always have candy in my pocket.

A positive-definite matrix is an important concept in linear algebra.

A positive-semidefinite matrix is one of the important concepts in linear algebra.