The equations became steadily longer and more complex. Then, abruptly, they simplified, only to begin a new deepening, simplify again, and finally become very complicated just at the end. The last few lines were obviously repetitious. Gradually, their meaning became clear to us. The first set of equations started off with simple, naturally-occurring energy yielding formulas. The oxidation of cellulose (we found the formula for that in an organic chemistry text left behind by one of the dome's previous occupants), which probably referred to the burning of plants and vegetation. A string of formulas that had groupings in them that I dimly recognized as amino acids--no doubt something to do with digesting food. There were many others, including a few that Rizzo claimed had the expression for chlorophyll in them. "Naturally-occurring, energy-yielding reactions," Rizzo summarized. "They're probably trying to describe the biological set-up on their planet." It seemed an inspired guess. * * * * * The second set of equations again began with simple formulas. The cellulose-burning reaction appeared again, but this time it was followed by equations dealing with the oxidation of hydrocarbons: coal and oil burning? A long series of equations that bore repeatedly the symbols for many different metals came up next, followed by more on hydrocarbons, and then a string of formulas that we couldn't decipher at all. This time it was my guess: "These look like energy-yielding reactions, too. At least in the beginning. But they don't seem to be naturally occurring types. Then comes a long story about metals. They're trying to tell us the history of their technological development--burning wood, coal and eventually oil; smelting metals ... they're showing us how they developed their technology." The final set of equations began with an ominous simplicity: a short series of very brief symbols that had the net result of four hydrogen atoms building into a helium atom. Nuclear fusion. "That's the proton-proton reaction," I explained to Rizzo. "The type of fusion that goes on in the Sun." The next series of equations spelled out the more complex carbon-nitrogen cycle of nuclear fusion, which was probably the primary energy source of their own Cepheid variable star. Then came a long series of equations that we couldn't decode in detail, but the symbols for uranium and plutonium, and some of the heavier elements, kept cropping up. Then came one line that told us the whole story: the lithium-hydride equation--nuclear fusion bombs. The equations went on to more complex reactions, formulas that no man on Earth had ever seen before. They were showing us the summation of their knowledge, and they had obviously been dealing with nuclear energies for much longer than we have on Earth.