Let be a function such that for any , ..., , there is at least one such that . Then the -operator gives the least number such that . More generally, for a relation , the -operator gives the least , if any, such that is true, and this least value of is denoted (Mendelson 1997, p. 175).
For example, given a criterion crit and a list x1, x2, ..., xn, the -operator could be written in the Wolfram Language as Select[Sort[x1, x2, ..., xn], crit, 1].