ula $A$,
|
|      and &quot;B&quot; by the formula obtained from $A$
|
|      by replacing each occurrence
|
|      of the variable which replaced !a!
|
|      by the variable which replaced !b!:
|
|      For each !b!, !b! in {!a! : A} if and only if !b! is a set and B.
|
| †  This circuitous sort of language is unfortunately necessary.
|    Using the convention of quotation marks for names, for example,
|    &quot;Boston&quot; is the name of Boston, if $A$ is a formula and $B$ is
|    a formula then &quo