Don Pigozzi. Base-undecidable properties of universal varieties. Algebra universalis, vol. 6 (1976), pp. 193–223. - Don Pigozzi. Universal equational theories and varieties of algebras. Annals of mathematical logic, vol. 17 (1979), pp. 117–150.
Stanley N. Burris · Journal of Symbolic Logic · 1982
Don Pigozzi. Base-undecidable properties of universal varieties. Algebra universalis, vol. 6 (1976), pp. 193–223. - Don Pigozzi. Universal equational theories and varieties of algebras. Annals of mathematical logic, vol. 17 (1979), pp. 117–150. - Volume 47 Issue 4