**3.1 Evolution trajectories**

The general principle is then to make the evolution of the system a process as continuous as possible. Practically, the evolution process is made up of a sequence of steps representing the evolution of the state of the system. The closer in time these steps are, the more continuous the evolution of the system will be. Two steps are specific. The first one corresponds to the state of the system at the time it is examined (t = 0). This step therefore corresponds to the *current state*. The second represents the state in which we would like the system to be in the future, at a time sufficiently far in the future but for which it is possible to make viable predictions about the system's environment. We refer to this step as the *target* and the moment at which it corresponds as the *strategic horizon*. The path between the current state and the target is punctuated by intermediate states that we call *steps*. These steps are the moments when the environment is reassessed and the target is redefined. If the environment has not changed, the target remains the same. This is equivalent to saying that the target is the desired state in the future, assuming the environment has not changed. However, we will consider that this is not the general case. Therefore, at each step, a new target is defined. The duration between two steps is usually fixed, we call this duration *strategic period*. It is clear that, because the steps are intended to be moments of redefinition of the target, the strategic period will be all the shorter as the environment changes rapidly.

**Figure 3** summarises these concepts.
