Union
$$A \cup B =$$
{ astronomy, biology, chemistry, electric, fossil, gravitational, hydric, mathematics, organic, physics, sociology, solar, thermal, wind }
Symmetric Difference
$$A \ominus B =$$
{ astronomy, biology, chemistry, electric, fossil, gravitational, hydric, mathematics, organic, physics, sociology, solar, thermal, wind }
Cartesian Product
$$A \times B =$$
{ (astronomy, electric),
(astronomy, fossil),
(astronomy, gravitational),
(astronomy, hydric),
(astronomy, organic),
(astronomy, solar),
(astronomy, thermal),
(astronomy, wind),
(biology, electric),
(biology, fossil),
(biology, gravitational),
(biology, hydric),
(biology, organic),
(biology, solar),
(biology, thermal),
(biology, wind),
(chemistry, electric),
(chemistry, fossil),
(chemistry, gravitational),
(chemistry, hydric),
(chemistry, organic),
(chemistry, solar),
(chemistry, thermal),
(chemistry, wind),
(mathematics, electric),
(mathematics, fossil),
(mathematics, gravitational),
(mathematics, hydric),
(mathematics, organic),
(mathematics, solar),
(mathematics, thermal),
(mathematics, wind),
(physics, electric),
(physics, fossil),
(physics, gravitational),
(physics, hydric),
(physics, organic),
(physics, solar),
(physics, thermal),
(physics, wind),
(sociology, electric),
(sociology, fossil),
(sociology, gravitational),
(sociology, hydric),
(sociology, organic),
(sociology, solar),
(sociology, thermal),
(sociology, wind) }
Law of three stages