This is the personal notebook of Albert Einstein when he was developing the general theory of relativity. In it, one can see the various nuanced techniques which he used to help him with his theory. Although having a humongous arsenal of mathematical techniques he did struggle with the non Euclidean geometry which was needed in this case to address the curving of the space time. All he had to do was to prove that the geometrical structure(tensors(generalized vectors)) were equal to the material mass which was the source of the bending of the fabric of the space time from which gravity emerged as the emergent phenomenon. Along with this in the margins of his notebook one can also see something rather silly but if one meditates about this become kind of obvious. Puzzles, the kind of puzzles which we set for children for their past time. The great Albert Einstein used to try his hands on those puzzles succeeding and failing both at various times in the margins of the same notebook which would certainly make him immortal and set his name synonym to genius. How remarkable that is! I mean just look how naive that puzzle looks in those margins drawn by the very hands of the legend himself. One more thing which clearly indicates of his non linear thinking approach as he wrote both upside and downside of the same page trying different approach for the same thing and trying to check if they really are the same or one can also notice as how at various intervals of time, he asks simple questions to himself like is thing invariant? and other trivial stuff. But the devil is in the details and in these trivial things lies the greatest of insights. History is the witness for this. The careful understanding of the trivial things are very important and that is what sets apart the genius from the herd. How the trivial nuances play a larger role in the big picture and trying to understand that machinery is the real game. Hope you were able to take away a thing or two from this.