Here is an **IN PROGRESS listing** of every area I have worked on, roughly in the order of adoption (most ancient first) :

**1. Formal Languages and Combinatorics on Words **

Results in formal language theory.

** 1. Contextual languages.**

to write.

** 2. Structural equivalence notions for L-systems.**

to write

Results in Combinatorics on Words.

**1. Self-reading sequences.**

to write.

**2. Recursive function theory, later Computational Complexity **

Effective category in recursive function theory.

** 1. Approximability of the Minimum Entropy Set Cover on sparse instances. **

MESC is a problem initially studied by Halperin and Karp (and Cardinal et al.), initially motivated by a problem from computational biology (haplotype resolution)In paper [2] we give a better approximation guarantee for sparse instances of MESC.

** 2. The Minimum Entropy Submodular Set Cover problem and its approximability. **

In paper [9] (chronologically the first we wrote on this topic) we generalize the problem to Minimal Entropy Submodular Set Cover (MESSC), a framework that captures many interesting combinatorial subproblems.We give a guarantee for the performance approximation guarantee of the GREEDY algorithm that is * almost as good * as the one available for (the same algorithm on) MESC