We call A weakly low for K if there is a c such that $K^A(\sigma)\geq K(\sigma)-c$ for infinitely many σ; in other words, there are infinitely
many strings that A does not help compress. We prove that A is
weakly low for K if and only if Chaitin's Ω is
A-random. This has consequences in the K-degrees and the low for
K (i.e., low for random) degrees. Furthermore, we prove that the
initial segment prefix-free complexity of 2-random reals is infinitely often
maximal. This had previously been proved for plain Kolmogorov complexity.