  Recently Tao, Croot and Helfgott invented an algorithm to determine the
parity of the number of primes in a given interval in O(x^{1/2-c+\eps}) steps
for some absolute constant c. We propose a slightly different approach, which
leads to the implicit value of c. To achieve this aim we discuss the summation
of multiplicative functions, developing sublinear algorithms and proving
several general theorems.
