PhD course on lattice-ordered groups and polyhedral geometry (Spring 2024)


The course is an introduction to the theory of abelian lattice-ordered groups from different perspectives. Initially, we study these structures with purely algebraic methods. We will analyse some important theorems and connections with other parts of mathematics, such as AF C*-algebras. Later we will move on to their geometric study, through the Baker-Beynon duality. It will be seen that, just as the commutative rings provide an algebraic counterpart for the study of affine manifolds with polynomial maps, lattice-ordered groups represent the algebraic counterpart of the polyhedral cones and piece-wise linear homogenous maps between them.

Course topics

  • Abelian lattice-ordered groups: definition and examples.
  • Representation results.
  • Archimedeanity and strong (order) unit.
  • Free and finitely presented abelian l-groups.
  • Baker&Beynon duality.
  • Mundici’s functor.
  • MV-algebras.
  • Polyhedral geometry.

Lecture by lecture topics

  • 19 March – Introduction to the course, overview of the contents, basic definitions and first properties. Lecture notes.
  • 22 March – Examples, l-homomorphisms and l-ideals. Lecture notes.
  • 26 March – Congruences and l-ideals. Prime l-ideals. Subdirect representation by linearly ordered l-groups. Lecture notes.
  • 27 March – Lexicographic products, Archimedean l-groups, Hölder theorem, Weinberg theorem. Lecture notes.
  • 4 April – General affine adjunctions. Example: Stone duality. Lecture notes.
  • 5 April – Unital l-groups, MV-algebras, a geometric duality for semi-simple MV-algebras. Lecture notes.
  • 9 April – Baker-Beynon duality Archimedean for l-groups. Lecture notes.
  • 11 April – Beyond Baker-Beynon duality: the duality for the whole class of l-groups. Luca Carai’s Slides.
  • 16 April – Polyhedral geometry: triangulations and unimodular triangulations. Lecture notes.
  • 18 April – Finitely generated projective l-groups. Yosida duality. Lecture notes.

Course material

  • Bigard, A., Keimel, K., & Wolfenstein, S. (2006). Groupes et anneaux réticulés (Vol. 608). Springer.
  • Anderson, M. E., & Feil, T. H. (2012). Lattice-ordered groups: an introduction (Vol. 4). Springer Science & Business Media.
  • Goodearl, K. R. (2010). Partially ordered abelian groups with interpolation (No. 20). American Mathematical Soc.
  • Glass, A. M. W. (1999). Partially ordered groups (Vol. 7). World Scientific.
  • Cignoli R., D’Ottaviano I. M. L., Mundici D. (2000) Algebraic Foundations of many-valued Reasoning, Trends in Logic, Vol. 7, Kluwer Academic Publishers.
  • Mundici, D. (2011). Advanced Łukasiewicz calculus and MV-algebras, Trends in Logic, Vol. 35 Springer.

Practical aspects

Term and schedule

Lecturer: Luca Spada
Course duration: 20 hours.
Course calendar: Lectures will all take place in room P18 from 9:30 to 11:30 in the following days: 19 March, 22 March, 26 March, 27 March, 4 April, 5 April, 9 April, 11 April, 16 April, 18 April.


You can choose to take the final exam in one of the following ways:

  • A short oral interview (about 30 minutes) in which the knowledge acquired on the basic and more advanced concepts will be evaluated.
  • The presentation of a topic agreed with the teacher and not covered in the course, in the form of a short seminar also open to other doctoral students lasting about 30 minutes.
  • Solving some exercises at home.

A(nother) duality for the whole variety of MV-algebras

This is the abstract of a talk I gave in Florence at Beyond 2014.

Given a category C one can form its ind-completion by taking all formal directed colimits of objects in C. The “correct” arrows to consider are then families of some special equivalence classes of arrows in C (Johnstone 1986, V.1.2, pag. 225). The pro-completion is formed dually by taking all formal directed limits. For general reasons, the ind-completion of a category C is dually equivalent to the pro-completion of the dual category C^{\rm op}.

$$\textrm{ind}\mbox{-}C\simeq (\textrm{pro}\mbox{-}(C^{\rm{op}}))^{\rm{op}}.       \qquad\qquad (1)$$

Ind- and pro- completions are very useful objects (as they are closed under directed (co)limits) but cumbersome to use, because of the involved definitions of arrows between objects. We prove that if C is an algebraic category, then the situation considerably simplifies.

If V is any variety of algebras, one can think of any algebra A in V as colimit of finitely presented algebras as follows.

Consider a presentation of A i.e., a cardinal \mu and a congruence [/latex]\theta[/latex] on the free \mu-generated algebra \mathcal{F}(\mu) such that A\cong \mathcal{F}(\mu)/\theta. Now, consider the set F(\theta) of all finitely generated congruences contained in \theta, this gives a directed diagram in which the objects are the finitely presented algebras of the form \mathcal{F}(n)/\theta_{i} where \theta_{i}\in F(\theta) and X_{1},...,X_{n} are the free generators occurring in \theta_{i}. It is straightforward to see that this diagram is directed, for if \mathcal{F}(m)/\theta_{1} and \mathcal{F}(n)/\theta_{2} are in the diagram, then both map into \mathcal{F}(m+n)/\langle\theta_{1}\uplus\theta_{2}\rangle, where \langle\theta_{1}\uplus\theta_{2}\rangle is the congruence generated by the disjoint union of \theta_{1} and \theta_{2}. Now, the colimit of such a diagram is exactly A.

Denoting by V_{\textrm{fp}} the full subcategory of V of finitely presented objects, the above reasoning entails

$$V\simeq\textrm{ind}\mbox{-}V_{\textrm{fp}}.        \qquad\qquad (2)$$

We apply our result to the special case where V is the class of MV-algebras. One can then combine the duality between finitely presented MV-algebras and the category P_{\mathbb{Z}} of rational polyhedra with \mathbb{Z}-maps (see here), with (1)  and (2) to obtain,

$$MV\simeq\textrm{ind}\mbox{-}MV_{\textrm{fp}}\simeq \textrm{pro}\mbox{-}(P_{\mathbb{Z}})^{\rm{op}}.  \qquad\qquad (3)$$

This gives a categorical duality for the whole class of MV-algebras whose geometric content may be more transparent than other dualities in literature. In increasing order of complexity one has that any MV-algebra:

  1. is dual to a polyhedron (Finitely presented case);
  2. is dual to an intersection of polyhedra (Semisimple case);
  3. is dual to a countable nested sequence of polyhedra (Finitely generated case);
  4. is dual to the directed limit of a family of polyhedra. (General case).

Here are the slides of this talk


Course on Many-Valued Logics (Autumn 2014)

This page concerns the course `Many-Valued Logics’, taught at the University of Amsterdam from September – October 2014. 

Contents of the page


The course covers the following topics:

  • Basic Logic and Monoidal t-norm Logic.
  • Substructural logics and residuated lattices.
  • Cut elimination and completions.
  • Lukasiewicz logic.

More specifically, this is the content of each single class:

  • September, 1: Introduction, motivations, t-norms and their residua. Section 2.1 (up to Lemma 2.1.13) of the Course Material 1.
  • September, 5: Basic Logic, Residuated lattices, BL-algebras, linearly ordered BL-algebras. Section 2.2 and 2.3 (up to Lemma 2.3.16) of the Course Material 1.
  • September, 8: Lindenbaum-Tarski algebra of BL, algebraic completeness. Monodical t-norm logic, MTL-algebras, standard completeness. The rest of Course Material 1 (excluding Section 2.4) and Course Material 2.
  • September, 12: Ordinal decomposition of BL-algebras. Mostert and Shield Theorem.  Course Material 3.
  • September, 15: Ordinal decomposition of BL-algebras (continued). Algebrizable logics and equivalent algebraic semantics.  Course Material 4.
  • September, 19: Algebrizable logics and equivalent algebraic semantics (continued).  Course Material 4.
  • September, 22: Algebrizable logics and equivalent algebraic semantics (continued): Leibniz operator and implicit characterisations of algebraizability.  Course Material 4.
  • September, 26: Leibniz operator and implicit characterisations of algebraizability (continued).  Course Material 4. Gentzen calculus and the substructural hierarchy. Course Material 5 (to be continued).
  • September, 29: Structural quasi-equations and $N_2$ equations. Residuated frames. Course Material 5 (Continued).
  • October, 3: Analytic quasi-equations, dual frames, and MacNeille completions. Course Material 5 (Continued).
  • October, 9: Atomic conservativity, closing the circle of equivalencies. Course Material 5 (Continued).
  • October, 10: Lukasiewicz logic and MV-algebras. Mundici’s equivalence. Course Material 6.
  • October, 17: The duality between semisimple MV-algebras and Tychonoff spaces. Course Material 7.

Course material

The material needed during the course can be found below.

The homework due during the course can be found below.




  • Classes run from the 1st of September until the 17th of October; there will be 14 classes in total.
  • There are two classes weekly.
  • Due to the high number of participants classrooms will change weekly, will always be updated with the right classrooms.

Grading and homeworks

  • The grading is on the basis of weekly homework assignments, and a written exam at the end of the course.
  • The homework assignments will be made available weekly through this page.
  • The final grade will be determined for 2/3 by homeworks, and for 1/3 by the final exam.
  • In order to pass the course, a score at least 50/100 on the final exam is needed.

More specific information about homework and grading:

  • You are allowed to collaborate on the homework exercises, but you need to acknowledge explicitly with whom you have been collaborating, and write the solutions independently.
  • Deadlines for submission are strict.
  • Homework handed in after the deadline may not be taken into consideration; at the very least, points will be subtracted for late submission.
  • In case you think there is a problem with one of the exercises, contact the lecturer immediately.

Course Description

Many-valued logics are logical systems in which the truth values may be more than just “absolutely true” and “absolutely false”. This simple loosening opens the door to a large number of possible formalisms. The main methods of investigation are algebraic, although in the recent years the proof theory of many-valued logics has had a remarkable development.

This course will address a number of questions regarding classification, expressivity, and algebraic aspects of many-valued logics. Algebraic structures as Monoidal t-norm based algebras, MV-algebras, and residuated lattices will be introduced and studied during the course.

The course will cover seclected chapters of the following books.

  • P. Hájek, ‘Metamathematics of Fuzzy Logic‘, Trends in Logic, Vol. 4 Springer, 1998.
  • P. Cintula, P. Hájek, C. Noguera (Editors). ‘Handbook of Mathematical Fuzzy Logic‘ – Volume 1 and 2. Volumes 37 and 38 of Studies in Logic, Mathematical Logic and Foundations. College Publications, London, 2011
  • R. L. O. Cignoli, I. M. L. D’Ottaviano e D. Mundici, ‘Algebraic Foundations of Many-Valued Reasoning‘, Trends in Logic, Vol. 7 Springer, 2000
  • D. Mundici. ‘Advanced Lukasiewicz calculus and MV-algebras‘, Trends in Logic, Vol. 35 Springer, 2011.


It is assumed that students entering this class possess

  • Some mathematical maturity.
  • Familiarity with the basic theory of propositional and first order (classical) logic.

Basic knowledge of general algebra, topology and category theory will be handy but not necessary.


Comments, complaints, questions: mail Luca Spada

Geometrical dualities for Łukasiewicz logic

This is the transcript of a featured talk given on the 15th of September 2011 at the XIX Congeresso dell’Unione Matematica Italiana held in Bologna, Italy.  It is based on a joint work with Vincenzo Marra of the University of Milan that was published in Vincenzo Marra and Luca Spada. The dual adjunction between MV-algebras and Tychonoff spacesStudia Logica 100(1-2):253-278, 2012. Special issue of Studia Logica in memoriam Leo Esakia (L. Beklemishev, G. Bezhanishvili, D. Mundici and Y. Venema Editors).  

The article develops a general dual adjunction between MV-algebras (the algebraic equivalents of Łukasiewicz logic) and subspaces of Tychonoff cubes, endowed with the transformations that are definable in the language of MV-algebras. Such a dual adjunction restricts to a duality between semisimple MV-algebras and closed subspaces of Tychonoff cubes. Further the duality theorem for finitely presented objects is obtained from the general adjunction by a further specialisation. The treatment is aimed at emphasising the generality of the framework considered here in the prototypical case of MV-algebras.

Geometrical dualities for Łukasiewicz logic

Duality, projectivity, and unification in Łukasiewicz logic and MV-algebras

We prove that the unification type of Lukasiewicz infinite-valued propositional logic and of its equivalent algebraic semantics, the variety of MV-algebras,is nullary. The proof rests upon Ghilardi’s algebraic characterisation of unification types in terms of projective objects, recent progress by Cabrer and Mundici in the investigation of projective MV-algebras, the categorical duality between finitely presented MV-algebras and rational polyhedra, and, finally, a  homotopy-theoretic argument that exploits  lifts of continuous maps to the universal covering space of the circle. We discuss the background to such diverse tools. In particular, we offer a detailed proof of the duality theorem for finitely presented MV-algebras and rational polyhedra – a fundamental result that, albeit known to specialists, seems to appear in print here for the first time.

Duality, projectivity, and unification in Łukasiewicz logic and MV-algebras


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