It's the lowest they could find. From section 5: The factor of 5 may be reduced to 4 + ε by assigning a larger fraction of time to algorithm C. The constants c

It's the lowest they could find. From section 5: The factor of 5 may be reduced to 4 + ε by assigning a larger fraction of time to algorithm C. The constants cp and dp will then be proportional to 1/ε. We were not able to further reduce this factor.