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, 4
We 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]