Derivation

The Erable derivation instructions are der and der1, they compute the derivative of a (list of) function(s) like the built-in instruction but do not evaluate numeric expressions (like $\sqrt{2}$ or $\frac{1}{2}$). der1 is used for derivation with respect to the variable contained in VX and takes only one argument (the function to derive). der is used with 2 arguments: the (list of) function(s) to derive at level 2 and the variable with respect to which you want to derive at level 1. If level 1 is a list, der returns the gradient of level 2:
2: 'X^2+2*X*LN(Y)-1/Y', 1: { X Y }
-> { '2*X+2*LN(Y)' '2*X*(1/Y)+1/Y^2' }
der returns djZ(X,Y,...) for the derivative of the user-defined function Z(X,Y,...) with respect to the j-th variable of z(x,y,...).
Examples:
Suppose that $x \rightarrow z(x)$ is the primitive of $\sqrt{x^3-1}$. Type 'Z(X)' X der, you get $\partial _1z(x)$ on the stack. Enter $\sqrt{x^3-1}$ and hit = then enter DEFINE. Now, you can type 'Z(X^2)' X der EVAL and get $2x\sqrt{(x^2)3-1}$.
Try 'Y(X,X^2)' X der.