Union
$$A \cup B =$$
{ concrete example, duel coding, elaboration, interleaving, interval, nominal, ordinal, ratio, retrieval, spaced practice }
Symmetric Difference
$$A \ominus B =$$
{ concrete example, duel coding, elaboration, interleaving, interval, nominal, ordinal, ratio, retrieval, spaced practice }
Difference
$$B - A =$$
{ concrete example, duel coding, elaboration, interleaving, retrieval, spaced practice }
Cartesian Product
$$A \times B =$$
{ (interval, concrete example),
(interval, duel coding),
(interval, elaboration),
(interval, interleaving),
(interval, retrieval),
(interval, spaced practice),
(nominal, concrete example),
(nominal, duel coding),
(nominal, elaboration),
(nominal, interleaving),
(nominal, retrieval),
(nominal, spaced practice),
(ordinal, concrete example),
(ordinal, duel coding),
(ordinal, elaboration),
(ordinal, interleaving),
(ordinal, retrieval),
(ordinal, spaced practice),
(ratio, concrete example),
(ratio, duel coding),
(ratio, elaboration),
(ratio, interleaving),
(ratio, retrieval),
(ratio, spaced practice) }
Level of measurement