Atiyah and Singer constructed
a Fréchet operator algebra 𝒫∞ by closing a set of zero order pseudodifferential
operators on a compact manifold X in the topology generated by all the
norms of the spaces L(Hs), s real. Each operator in 𝒫∞ has a ‘symbol’, a
function in C(S∗X). Contradicting a statement of Atiyah and Singer and
establishing the manifold analogue of a conjecture by H. O. Cordes, it will
be shown that each function in C(S∗X) is the symbol of an operator in
𝒫∞.