The `op` operator takes either a ` set`, `list` (`array`) or `string` and returns the sequence of expressions
formed by removing the outermost braces (`set`), square
brackets (`list`) or single quotes (`string`).

> weekdays := ['monday', 'tuesday', 'wednesday', 'thursday', > 'friday']; # a list weekdays := [monday, tuesday, wednesday, thursday, friday] > op(weekdays); monday, tuesday, wednesday, thursday, friday # a string > op(weekdays[1]); monday > numbers := {1, 2, 3, 4}; # a set numbers := {1,2,3,4} > op(numbers); 1, 2, 3, 4We can exploit this operator to combine two lists into a single new list.

> weekdays := ['monday', 'tuesday', 'wednesday', 'thursday', 'friday']: > weekends := ['saturday', 'sunday']: > week := [ op(weekdays), op(weekends) ]; week := [monday, tuesday, wednesday, thursday, friday, saturday, sunday]