Iverson Bracket

In mathematics, the Iverson bracket, named after Kenneth E. Iverson, is a notation that denotes a number that is 1 if the condition in square brackets is satisfied, and 0 otherwise. More exactly,

where P is a statement that can be true or false. This notation was introduced by Kenneth E. Iverson in his programming language APL, while the specific restriction to square brackets was advocated by Donald Knuth to avoid ambiguity in parenthesized logical expressions.