quality:corruption, structural:expansion
Mnemonic

The word "xyzzy" can be used to remember the definition of the cross product.

If

where:

then:

The second and third equations can be obtained from the first by simply vertically rotating the subscripts, x → y → z → x. The problem, of course, is how to remember the first equation, and two options are available for this purpose: either to remember the relevant two diagonals of Sarrus's scheme (those containing i), or to remember the xyzzy sequence.

Since the first diagonal in Sarrus's scheme is just the main diagonal of the above -mentioned 3×3 matrix, the first three letters of the word xyzzy can be very easily remembered.