The third diagram, ‘systematic production of alternatives’, shows a designer who is consciously setting up several alternative approaches and exploring them before using critical judgement to make a decision. The fourth diagram, ‘forming alternatives in a multi-step process’, describes a designer who will develop multiple solutions but with self-imposed constraints to reduce the number of alternatives to a manageable amount. In theory, this linear process could describe a very experienced architect who is solving a problem similar to previous, successfully solved ones. However, when applied to architectural problems, this makes the assumption that an architect would wish to solve a similar problem in a similar way rather than to continually seek innovation, as most would strive to do. However, it is impossible to use such diagrams to provide a definitive record of the actual process followed. In his book Tools for Ideas: Introduction to Architectural Design, Christian Ganshirt shows four alternative diagrams that Horst Rittel used to describe the design process. When this does not produce the desired result, the designer returns to the beginning and tries a different solution. The second diagram, ‘testing and scanning’, shows an attempt by the designer to use the first solution that occurs to them. The first and simplest diagram, a ‘linear sequence’, shows activity followed by a decision, which leads to further activity, which leads in turn to another decision and so on.