The help page for  PDEtools,dsubs  says  "dsubs will substitute the left hand side of each substitution equation until this derivative is eliminated from the target"

Trying a subs like u'=u into the expression u'' gives u -- as it should:

PDEtools:-dsubs(diff(u(x),x) = u(x), diff(u(x),x,x));


Substituting u'=u  into the expression  u''' should give u, but doesn't:

PDEtools:-dsubs(diff(u(x),x) = u(x), diff(u(x),x,x,x));
                                  --- u(x)

So how come du/dx hasn't been fully substituted as claimed by dsubs docs?  It looks like a bug...


I'm using Maple 11.


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