aref

(aref array &rest subscripts)

Returns the element of array at the given 0-based subscripts, one per dimension (one for a rank-1 vector, two for a rank-2 array, and so on). Flat rank-independent access is available via row-major-aref. To modify an element, use aref as a setf place: (setf (aref array i j) value), which also works with incf/decf/push. aref is not exposed as a first-class function value (#'aref is unavailable), so call it directly.