Union
$$A \cup B =$$
{ electric, enclosure, fossil, gravitational, hearth, hydric, mound, organic, roof, solar, thermal, wind }
Symmetric Difference
$$A \ominus B =$$
{ electric, enclosure, fossil, gravitational, hearth, hydric, mound, organic, roof, solar, thermal, wind }
Difference
$$B - A =$$
{ electric, fossil, gravitational, hydric, organic, solar, thermal, wind }
Cartesian Product
$$A \times B =$$
{ (enclosure, electric),
(enclosure, fossil),
(enclosure, gravitational),
(enclosure, hydric),
(enclosure, organic),
(enclosure, solar),
(enclosure, thermal),
(enclosure, wind),
(hearth, electric),
(hearth, fossil),
(hearth, gravitational),
(hearth, hydric),
(hearth, organic),
(hearth, solar),
(hearth, thermal),
(hearth, wind),
(mound, electric),
(mound, fossil),
(mound, gravitational),
(mound, hydric),
(mound, organic),
(mound, solar),
(mound, thermal),
(mound, wind),
(roof, electric),
(roof, fossil),
(roof, gravitational),
(roof, hydric),
(roof, organic),
(roof, solar),
(roof, thermal),
(roof, wind) }
The Four Elements of Architecture