Usage: x = traceQS(A [,i1,i2])
trace out index set i1 with i2 of given QSpace object;
for even-rank A, missing index sets is interpreted as
full trace of indices i1=1:r/2 with iw=r/2+1:r.
if all indices of A are traced out, the returned x is
a number (QSpace otherwise).
AW (C) 2006 ; 2018