This time negation is used to tag the numbers as it is
stated in the algorithm. Programs A and B used symbols
not numbers.
The \mb{PB..} instructions in lines 05 and 11 are based on the
assumption that $C\leq N/2$. Later the analysis of $C$ in the
book shows that the assumption is correct.
The program needs $4N\mems + (12N+5C+5)\oops$. The execution
with the test data gives the statistic for \mb{Invert}:
{\tt 78 instructions, 24 mems, 92 oops; 11 good guesses, 7 bad}.
As in this case $N=6$ and $C=3$ the above formula calculates
24\mems\ and $72+15+5\oops=92\oops$ in agreement with the measured data.