This book constitutes the refereed proceedings of the 21st International Symposium on Mathematical Foundations of Computer Science, MFCS '96, held in Crakow, Poland in September 1996.
The volume presents 35 revised full papers selected from a total of 95 submissions together with 8 invited papers and 2 abstracts of invited talks. The papers included cover issues from the whole area of theoretical computer science, with a certain emphasis on mathematical and logical foundations. The 10 invited presentations are of particular value.

The origins of relational theories can be found in the work of three 19th cen- tury mathematicians: Augustus de Morgan (1864, On the syllogism IV and on the logic of relations), Charles Sanders Peirce (1882, Brief description of the algebra of relatives) and Ernst Schroder (1895, Vorlesungen iiber die Al- gebra und Logik der Relative). The modern origins of the theory of relations are due to Alfred Tarski (14 January 1902, Warsaw -26 October 1983, Berke- ley). His paper' On the calculus of Relations' published in 1941 gave rise to an algebraic theory of relations which is still extensively...