To install this package, run in Emacs:
M-x package-install RET seq RET
Sequence-manipulation functions that complement basic functions provided by subr.el. All functions are prefixed with "seq-". All provided functions work on lists, strings and vectors. Functions taking a predicate or iterating over a sequence using a function as argument take the function as their first argument and the sequence as their second argument. All other functions take the sequence as their first argument.