From the opposite point of view, Child thought that the ballad "must be of considerable age", even though the earliest available to him was datable only to ca. 1700–1750. E. B. Lyle, who has published extensively on Thomas the Rhymer, presents the hypothesis that the ballad had once existed in a very early form upon which the romance was based as its source. One supporter of this view is Helen Cooper who remarks that the ballad "has one of the strongest claims to medieval origins"; another is Richard Firth Green who states that "continuous oral transmission is the only credible explanation". However, both Cooper and Green draw these conclusions under the mistaken assumption that the "romance... had not yet been printed at the time of Mrs Brown's performance".