  A canonical system of basic invariants is a system of invariants satisfying a
set of differential equations. The properties of a canonical system are related
to the mean value property for polytopes. In this article, we naturally
identify the vector space spanned by a canonical system of basic invariants
with an invariant space determined by a fundamental antiinvariant. From this
identification, we obtain explicit formulas of canonical systems of basic
invariants. The construction of the formulas does not depend on the
classification of finite irreducible reflection groups.
