[Maxima] Mixed directional derivative

[Olumide]

Hello,

I'm still new to Maxima ... I would like use Maxima to write out the 
mixed directional derivatives like (grad(grad C).a).b, where a and b are 
vectors and C(x,y,z) is a scalar function.

Please visit http://en.wikipedia.org/wiki/Del#Directional_derivative for 
  an example of a first-order directional derivative.

Thanks,

- Olumide