## Tuesday, January 24, 2023

### Euclid's Elements

Nothing to do with cells and networks, but I have an interest in Euclid's Elements and decided to publish a new edition of Book I. The difference with previous editions is that this one is in color and also has a chapter on the history of the elements, together with commentaries on each proposition. For those unfamiliar with Euclid's Elements, it's a series of books (more like chapters in today's language) laying the foundation for geometry and number theory. Book I focuses on the foundation of geometry culminating in a proof for Pythagoras' theorem and other important but less known results. The key innovation is that it describes a deductive approach to geometry. It starts with definitions and axioms from which all results are derived using logical proofs.

It occurred to me that something similar could be done with deriving the properties of biochemical networks. For example, we might define the following three primitives:

I. Species

II. Reaction

We might then define the following axioms:

I. A species has associated with it a value called the concentration, x_i.

II. All concentrations are positive.

III. A reaction has a value associated with it called the reaction rate, v_i.

IV. Reaction rates can be negative, zero, or positive.

V. A reaction transforms one or more species (reactants) into one or more other species (products).

VI. The reaction rate is a continuous function of the reactants and products.

VII. The rate of change of a species can be described using a differential equation, dx/dt

VIII. All steps are reversible unless otherwise stated (may this can be derived?)

etc

Given these axioms, we could build a series of propositions. This might be an interesting exercise to do. Some of the more obvious propositions would be the results from metabolic control analysis, such as the summation and connectivity theorems.