However, that runs counter to the thinking behind the waterfall approach: Many design teams would view modifying the design after Stage 1 as a failure of their initial design or requirements process.

At a later stage, the commodities also developed derivatives contracts, with consumers and producers hedging the risk of volatile prices with over-the-counter swaps and, later, futures contracts.

On the basis of material balance, a model of two-stage underground coal gasification in counter directions is built with ideal gasification parameters.