  In the last decades, several objects such as grammars, economical agents,
laws of physics... have been defined as algorithms. In particular, after
Brouwer, Heyting, and Kolomogorov, mathematical proofs have been defined as
algorithms. In this paper, we show that mathematical theories can be also be
defined as algorithms and that this definition has some advantages over the
usual definition of theories as sets of axioms.
