I can't make sense of any of that. Does Aijkl=Fijkl(am) mean that Aijkl is the result of letting Fijkl act on am? Then why doesn't A have five indices instead of four? Is am a vector or a component of a vector? Why doesn't m appear anywhere on the right? What are the definitions of A·B and A-1? (I haven't seen either defined for tensors with 4 indices). Does A denote the tensor and Aijkl its components in a coordinate system? Then what does A (no indices, not bold) denote?
Looks to me like F just takes a six-tuple of coefficients (what kind, who knows?) and spits out a rank-4 tensor. In other words, F is some six-parameter family of tensors. I suppose the answers will be in terms of the a_i's and b_i's (i=1,...,6).