array-in-bounds-p

(array-in-bounds-p array &rest subscripts)

Returns true when every subscript is a valid index into array, nil otherwise -- without signaling. A non-array, a subscript count that does not match the rank, and any negative or out-of-range subscript all answer nil. Strings count (they are rank-1 character arrays); the dimension, not the fill pointer, is what a subscript is checked against.