order. @ uses the integer values on the right to index into the original list of strings. A function to determine if a number is prime can be written as: {&/x!/:2_!x} The function is evaluated from right to left: !x enumerate the positive integers less than x. 2_ drops the first two elements of the enumeration (0 and 1). x!/: performs modulo division between the original integer and each value in the truncated list. &/ find the minimum value of the list of modulo result. If x is not prime then one of the values returned by the modulo operation will be 0 and consequently the minimal value of the list. If x is prime then the minimal value will be 1, because x mod 2 is 1 for any prime greater than 2. The function below can be used to list all of the prime numbers between 1 and R with: 2_&{&/x!/:2_!x}'!R The expression is evaluated from right to left !R enumerate the integers less than R. ' apply each value of the enumeration to the prime number function on the left. This will return a list of 0's and 1's. & return the indices of the list where the value is 1. 2_ drop the first two elements of the enumeration (0 and 1) K financial products K is the foundation for a family of financial products. Kdb+ is an in-memory, column-based database with much of the same functions of a relational database management system. The database supports SQL, SQL-92 and ksql, a query language with a syntax similar to SQL and designed for column based queries and array analysis. Kdb+ is available for several operating systems, including Solaris, Linux, macOS, and Windows (32-bit or 64-bit). See also J, another APL-inspired language Q, the language of kdb+ and a new merged version of K and ksql. References External links , Kx Systems , kdb+ Overview of K (with a link to K reference card) Dennis Shasha - K as a Prototyping Language Michael Schidlowsky - Screencast comparing solutions of a specific problem in K vs. Java K by Arthur Whitney (2005) oK REPL for a K clone Kona an open-source K3 implementation APL programming language family Array programming languages Data-centric programming languages Dynamic programming languages Function-level languages Proprietary database management systems Programming languages Dynamically typed programming languages High-level programming languages 1993 software Programming languages created in 1993