I have a large system of non-linear equations. Is there any way to get Maple to remove the duplicate equations in the system? For example Maple doesn't recognise that x-y =0 is equal to y-x=0. 

Say I have a polynomial x^5 + 4xy^4 + 2y^3 +  x*y^2 + x^2 + y + 3

Can I truncate it up to total degree 3 (for example), so 2y^3 +  x*y^2 + x^2 + y + 3

How do I differentiate with respect to lnx? So for example df(x)/d lnx = xdf(x)/dx

What I am specifically after is a way to obtain d^n f(x)/d (lnx)^n (or equivalently (x*d/dx)^n f(x) ) so simply writing df(x)/d lnx = x*diff(f(x),x) is no good.

I have a set of around 60 linear equations with symbolic coefficients. ie

a*x₁ + b*x₂ + ... + c*x₆₀ = 1

x₁ + (c-a)*x₂ + ... + d*x₆₀ = 0

...

c*x₁ + d*x₂ + ... + b*x₆₀ = a

The coefficients a,b,c,d are functions of x₁...x₆₀. I am trying to find the values of these coefficients. When I had a smaller set of equations I was solving them symbolically to find x₁...x₆₀ in terms of a,b,c,d and then using this solution to solve for a,b,c,d. I can no longer solve the set of equations symbolically as it is too large. How do I find the coefficients? I had some sort of optimization routine in mind.