As one door closes, another opens.

Closed systems are commonly used in scientific experiments.

Bicartesian closed categories are an important concept in category theory.

The boot closers are responsible for securing the boots.

Cartesian closed categories are an important concept in category theory.

There are many closed cities in Russia.

There are several close stooles in the antique shop.

I bought a set of close-up lenses for my camera.

The closed balls in the set are all of the same size.

Closed curves are often used in mathematics to represent shapes.