initially,

First, in Section 3.2, we examine the relationship between catastrophe theory and the theory of differential equations and begin to see that, in applied work, the two branches will work hand in hand. In Section 3.3, we follow through an idea introduced earlier that it is irrportant to study explicitly the different rates of change of variables in a nudel and to use this as the basis for distinguishing different types of variables. This idea is used as a basis to draw together SOIre notions on system description.