ct' of $A$’ to $L$.  Sometimes we use the shorter
| notation ($A$, $I$’) for $A$’.  Clearly, there are many
| ways a model $A$ for $L$ can be expanded to a model
| $A$’ for $L$’.  On the other hand, given a model
| $A$’ for $L$’, it has only one reduction $A$ to
| $L$.  Namely, we form $A$ by restricting the
| interpretation function $I$’ on $L$ |_| X
| to $L$.  The processes of expansion and
| reduction do not change the universe
| of the model.
|
| The 'cardinal', or 'power', of the model 