With regard to (19c), the logical independence between at-issue content and CI can be verified by "yes, but…" test in (20)-(21) (Karttunen and Peters, 1979;Potts, 2005).
the response "yes, but…" disputes only the CI content, but not the at-issue content.the "yes" in B's utterance agrees with the truth value of the atissue content (i.e.