An important extension to Porter's work came from Adam Brandenburger and Barry Nalebuff of Yale School of Management in the mid-1990s. Using game theory, they added the concept of complementors (also called "the 6th force") to try to explain the reasoning behind strategic alliances. Complementors are known as the impact of related products and services already in the market. The idea that complementors are the sixth force has often been credited to Andrew Grove, former CEO of Intel Corporation. Martyn Richard Jones, while consulting at Groupe Bull, developed an augmented five forces model in Scotland in 1993. It is based on Porter's Framework and includes Government (national and regional) as well as pressure groups as the notional 6th force. This model was the result of work carried out as part of Groupe Bull's Knowledge Asset Management Organisation initiative.