@Mac Dude 

Hello,

Sorry if my initial post wasn't very clear.  I'm trying to define a system of differential equations, e.g.

dx/dt=x^2+y^2

dy/dt=x^2+y^2;

 as individual functions in maple.  So one function for dx/dt and one for dy/dt.  Ideally in Maple I would like to define something of the form

x'(t) := x(t)^2+y(t)^2:

y'(t) := x(t)^2-y(t)^2:

where x'(t) and y'(t) are functions I can re-use later in different contexts.  Specifically here I'm trying to use them to find the Jacobian of the linearised system about a given point.  That's essentially what this:

was an attempt at.  I used diff from the Physics package because it allows me to differentiate WRT the function x(t).