© 2001 by London Mathematical Society
Extensions of Pure States and Projections of Norm One II
Department of Mathematical Sciences, University of Aberdeen, King's College Aberdeen AB24 3UE; e-mail: r.archbold{at}maths.abdn.ac.uk
Received 5 November 1999. Revision received 29 February 2000.
It is shown that if a C*-algebra A contains a semi-scattered C*-algebra B such that the pure states of B and the zero functional extend uniquely to A, and the canonical mapping B^
 is injective, then there exists a (unique) projection of norm one R: A
B. In certain circumstances, the conditional expectation R can be effected by a unitary averaging process using unitary elements in the centre of the multiplier algebra M(B).