**This is an old revision of the document!**

## Mathematical Structures

The webpages collected here list information about classes of mathematical structures. The aim is to have a central place to check what properties are known about these structures.

These pages are currently still under construction.

Initially the main content concerns mostly first-order classes of relational structures and, more particularly, equationally defined classes of algebraic structures. If you are familiar with some of these classes of structures and would like some information added, please email Peter Jipsen (jipsen@chapman.edu). [Account creation unfortunately had to be disabled.]

**New:** Boldface links below display lists of finite algebras in a particular class (calculated locally in the browser).

Acknowledgements | Notation and terminology | Properties | Tools | Online books and lecture notes

Varieties | Quasivarieties | Universal classes | First-order classes | Second-order classes

Algebras | Logics | Syntax | Terms | Equations | Horn formulas | Universal formulas | First-order formulas

#### Alphabetical list of all classes

- BCI-algebras nbsp BCI algebra
- BCK-algebras nbsp BCK algebra