In Handbook of Philosophical Logic M. Dunn formulated a problem of describing pretabular extensions of relevant logics (cf. M. Dunn , p. 211; M. Dunn, G. Restall , p. 79). The main result of this paper is described in the title.
"There exists an uncountable set of pretabular extensions of the relevant logic R and each logic of this set is generated by a variety of finite height." J. Symbolic Logic 73 (4) 1249 - 1270, December 2008. https://doi.org/10.2178/jsl/1230396916