An algebra $$\mathbf{A}$$ is called a perfect extension of its subalgebra $$\mathbf{B}$$ if every congruence has unique to . This terminology was used by Blyth and Varlet [1994]. In the case lattices, this concept described Grätzer Wehrung [1999] saying that congruence-preserving Not many investigations have been carried out so far. The present authors in another recent study faced question whe...

The modern phase in Logic begins in the middle of the 19th century with the work of Frege, Boole, de Morgan and Peirce. A second phase began in the early 20th century with Russell’s discovery of his paradox, followed by Hilbert’s program to try (unsuccessfully) to get around it. Finally, the thirties saw fundamental developments by Gödel, Turing, Post, Church and Tarski. By this time, the follo...