Walter Dnes asked,
| Are the following two conditions...
| *$!^(Sender|From|Reply-To):.*$MYISP
| *$!^(To|Cc|Bcc):.*$LOGNAME
|
| when AND'ed, identical to...
| *$!^((Sender|From|Reply-To):.*$MYISP)|((To|Cc|Bcc):.*$LOGNAME))
You're on the right track, but you have a typo and imbalanced parentheses.
They're equivalent to
*$!^((Sender|From|Reply-To):.*$MYISP|(To|Cc|Bcc):.*$LOGNAME)
or if you prefer to repeat the caret,
*$!^(Sender|From|Reply-To):.*$MYISP|^(To|Cc|Bcc):.*$LOGNAME
because not (A or B) = (not A) and (not B)