Union
$$A \cup B =$$
{ adventure, art, beauty, enclosure, hearth, mound, peace, roof, truth }
Symmetric Difference
$$A \ominus B =$$
{ adventure, art, beauty, enclosure, hearth, mound, peace, roof, truth }
Difference
$$A - B =$$
{ enclosure, hearth, mound, roof }
Difference
$$B - A =$$
{ adventure, art, beauty, peace, truth }
Cartesian Product
$$A \times B =$$
{ (enclosure, adventure),
(enclosure, art),
(enclosure, beauty),
(enclosure, peace),
(enclosure, truth),
(hearth, adventure),
(hearth, art),
(hearth, beauty),
(hearth, peace),
(hearth, truth),
(mound, adventure),
(mound, art),
(mound, beauty),
(mound, peace),
(mound, truth),
(roof, adventure),
(roof, art),
(roof, beauty),
(roof, peace),
(roof, truth) }
The Four Elements of Architecture