Cardinal characteristics of the ideal of Haar null sets
We calculate the cardinal characteristics of the -ideal of Haar null subsets of a Polish non-locally compact group with invariant metric and show that . If is the product of abelian locally compact groups , then , , and , where is the ideal of Lebesgue null subsets on the real line. Martin Axiom implies that and hence contains a Haar null subset that cannot be enlarged to a Borel or projective Haar null subset of . This gives a negative (consistent) answer to a question of...