normal line to a surface at a point

tangent plane to a surface at a point

section a-a a-a

A-A-A conjugation structure

class a surface A

S-A(A-A) missile

A.A.A.

magnetic refrigeration at room temperature

simple refraction

a bomb blast at a phone booth

A cat may look at a king

action at a distance

Action-at-a-distance

ammonia synthesis at at-mospheric pressure and low temperature

at a

at a dash

at a disadvantage

at a discount

at a distance