104 4. MAXIMUM PRINCIPLES
A nice presentation of the scalar maximum principle for generalized heat
equations may be found on pages 101 - 102 of [56]. The maximum princi-
ple for tensor equations (Theorem 4.6) first appeared in [58]. The tensor
maximum principle for systems (Theorem 4.8) appeared in [5 9 ]. Maximum
principles for systems with time-dependent convex sets (Theorem 4.9) and
avoidance sets (Theorem 4.10) are studied in [33]. Certain maximum prin-
ciples of these types are used implicitly in some of Hamilton's work.
A reader interested in discussions of maximum principles for more gen-
eral classes of equations is encouraged to consult [ 110 ] and [121].