delete-duplicate-lines is an interactive autoloaded compiled Lisp function in `
(delete-duplicate-lines BEG END &optional REVERSE ADJACENT KEEP-BLANKS INTERACTIVE)
Delete all but one copy of any identical lines in the region.
Non-interactively, arguments BEG and END delimit the region.
Normally it searches forwards, keeping the first instance of
each identical line. If REVERSE is non-nil (interactively, with
a C-u prefix), it searches backwards and keeps the last instance of
each repeated line.
Identical lines need not be adjacent, unless the argument
ADJACENT is non-nil (interactively, with a C-u C-u prefix).
This is a more efficient mode of operation, and may be useful
on large regions that have already been sorted.
If the argument KEEP-BLANKS is non-nil (interactively, with a
C-u C-u C-u prefix), it retains repeated blank lines.
Returns the number of deleted lines. Interactively, or if INTERACTIVE
is non-nil, it also prints a message describing the number of deletions.