Union
$$A \cup B =$$
{ action, contemplation, gas, liquid, maintenance, plasma, precontemplation, preparation, solid, termination }
Symmetric Difference
$$A \ominus B =$$
{ action, contemplation, gas, liquid, maintenance, plasma, precontemplation, preparation, solid, termination }
Difference
$$A - B =$$
{ action, contemplation, maintenance, precontemplation, preparation, termination }
Cartesian Product
$$A \times B =$$
{ (action, gas),
(action, liquid),
(action, plasma),
(action, solid),
(contemplation, gas),
(contemplation, liquid),
(contemplation, plasma),
(contemplation, solid),
(maintenance, gas),
(maintenance, liquid),
(maintenance, plasma),
(maintenance, solid),
(precontemplation, gas),
(precontemplation, liquid),
(precontemplation, plasma),
(precontemplation, solid),
(preparation, gas),
(preparation, liquid),
(preparation, plasma),
(preparation, solid),
(termination, gas),
(termination, liquid),
(termination, plasma),
(termination, solid) }
Transtheoretical model