In mathematics, equivalence classes are a very important concept.

Polychaete worms play an important role in the seabed ecosystem.

The government declared a state of emergency to prevent the spread of the new coronavirus.

Tamaki is my best friend.

Tamami is my best friend.

Tamiko is my best friend.

Taichi is my best friend.

Kota, have you finished your homework for today?

Shota is my best friend.

This is a multipurpose tool.