An identity matrix is a square matrix in which all the elements on the diagonal are 1 and all other elements are 0.

The calculation of determinants is an important part of mathematics.

He lost everything.

The success of this project is a combination of many components.

He is brushing his lower teeth.

He smiled, showing his lower teeth.

She seemed nervous, biting her lower lip.

She seemed nervous, biting her lower lip.

He was complaining about pain in his armpit.

I plan to spend the afternoon at the library.