Our task is to build a mathematical model of a market of financial securities.
A crucial first stage is concerned with the properties of the mathematical
objects involved. This is done below by specifying a number of assumptions,
the purpose of which is to find a compromise between the complexity of the
real world and the limitations and simplifications of a mathematical model,
imposed in order to make it tractable. The assumptions reflect our current
position on this compromise and will be modified in the future.