[Radim]

> invert the problem and see if it's solvable by retracing from solution to the start

This last bit I personally find tremendously useful. It works best on hard conceptual blocks (though not necessarily Shannon-hard).

I start by "explaining" to an invisible audience how I solved (past tense) the problem – without having a clue how to actually approach it. First the overall hand-wavy "feel" of the solution, then filling in more specific gaps as the imaginary audience prompts. Sometimes retracting and adjusting the narrative. Very top-down, back-to-front.

By the end of this, there's often a working outline. I call it "Solution by Bragging", as a more extreme form of rubber-ducking.

[theoh]

That's not what Shannon means. He just meant "solve the inverse problem".