extremum (sequence predicate &key key start end)

Returns the element of SEQUENCE that would appear first if the subsequence bounded by START and END was sorted using PREDICATE and KEY.

EXTREMUM determines the relationship between two elements of SEQUENCE by using the PREDICATE function. PREDICATE should return true if and only if the first argument is strictly less than the second one (in some appropriate sense). Two arguments X and Y are considered to be equal if (FUNCALL PREDICATE X Y) and (FUNCALL PREDICATE Y X) are both false.

The arguments to the PREDICATE function are computed from elements of SEQUENCE using the KEY function, if supplied. If KEY is not supplied or is NIL, the sequence element itself is used.

If SEQUENCE is empty, NIL is returned.