Union
$$A \cup B =$$
{ arithmetic, astronomy, earth, geometry, grass, heaven, lake, mountain, music, river, thunder, wood }
Symmetric Difference
$$A \ominus B =$$
{ arithmetic, astronomy, earth, geometry, grass, heaven, lake, mountain, music, river, thunder, wood }
Difference
$$B - A =$$
{ earth, grass, heaven, lake, mountain, river, thunder, wood }
Cartesian Product
$$A \times B =$$
{ (arithmetic, earth),
(arithmetic, grass),
(arithmetic, heaven),
(arithmetic, lake),
(arithmetic, mountain),
(arithmetic, river),
(arithmetic, thunder),
(arithmetic, wood),
(astronomy, earth),
(astronomy, grass),
(astronomy, heaven),
(astronomy, lake),
(astronomy, mountain),
(astronomy, river),
(astronomy, thunder),
(astronomy, wood),
(geometry, earth),
(geometry, grass),
(geometry, heaven),
(geometry, lake),
(geometry, mountain),
(geometry, river),
(geometry, thunder),
(geometry, wood),
(music, earth),
(music, grass),
(music, heaven),
(music, lake),
(music, mountain),
(music, river),
(music, thunder),
(music, wood) }
Quadrivium