(a) if it is difficult or impracticable for the Chief Commissioner
to determine a person's tax liability under a taxation law without undue delay
or expense because of the complexity or uncertainty of the case or for any
other reason, or
(b) for the purpose of settling a dispute between the
Chief Commissioner and a person concerning the person's tax liability (whether
or not a previous assessment has been made).
(2) The Chief Commissioner may,
with the agreement of the taxpayer, assess liability in an amount specified
in, or determined in accordance with, the agreement.
(3) Despite section 9,
the Chief Commissioner cannot make a reassessment of a tax liability assessed
in accordance with this section--