Named after Kenneth E. Iverson, who introduced this notation in his programming language APL.
Iverson bracket (plural Iverson brackets)
(mathematics) A notation that denotes a number that is 1 if the condition in square brackets is satisfied, and 0 otherwise, i.e.
(where P is a true or false statement)
[P]=\left\{\begin{array}{ll} 1 & \text { if } P \text { is true; } \\ 0 & \text { otherwise. } \end{array}\right.