Plot tan, cot, sec and csc on the interval [-2Pi, 2Pi]. (Note that these functions all have vertical asymptotes.) You should know these graphs well. The trigonometeric functions are all periodic, that ...

Thus {f, g} represents the unordered pair of functions f and g. So will plot both f and g on the same graph. We don't care wich order it does them in so we can give f and g as an unordered pair.