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Top1. Introduction
Group creativity techniques, e.g., brainstorming (Osborn, 1953), have been widely studied in social science (Nemeth, 1986; Paulus, 2000). A cooperative group contains multiple individuals who have some interactions on ideas of each other’s (Paulus, 2000), and the group tries to find innovative solutions (or high-quality ideas) for a specific task by generating new (especially innovative) ideas spontaneously contributed by its members in iterative idea-generating sessions.
Group creativity has been studied in both group and individual levels. At the group level, a support mechanism is used to assist individuals by providing useful external stimulus in their idea-generation process. The essential function of these mechanisms is to serve as group memory (Betts & Hinsz, 2010; Satzinger, Garfield, & Nagasundaram, 1999) for the diffusion of innovative patterns (Rogers, 2003) as well as providing diverse ideas (Paulus, 2000), based on a developing repository of nonprivate knowledge shared by members. For individuals, group memory might be heterogeneously shaped in network structures (Lovejoy & Sinha, 2010; Rulke & Galaskiewicz, 2000).
For each individual, the ideation process involves idea selection (Rietzschel, Nijstad, & Stroebe, 2010; Putman & Paulus, 2009) and idea generation (Nijstad & Stroebe, 2006; Paulus, 2000; Kohn, Paulus, & Choi, 2011), based on its individual memory (Glenberg, 1997; Newell & Simon, 1972). A pre-selection mechanism (Putman & Paulus, 2009) might be used to pick out relevant ideas from both the individual and group memory. Then an idea-generation mechanism is used to build new idea(s) on selected ideas. Afterward, a post-selection mechanism (Rietzschel et al., 2010) is applied to update the individual memory. Each individual also holds a sharing mechanism to contribute nonprivate knowledge (Liu & Tsui, 2006) for the group.
The idea-generation process is a critical part of the creative process. Since the research of Osborn (1953), combine-and-improve ideas has been a general brainstorming rule to form a single better idea by building on existing ideas. The total process of building on existing ideas might be divided into two parts, the idea combination process (Kohn et al., 2011; Yu & Nickerson, 2011) and the idea improvement process, roughly corresponding to the divergent and convergent processes, where the former is of paramount importance although the latter is also nontrivial (Cropley, 2006).
Human problem solving can be seen as searching in a structural space of states (ideas) (Newell & Simon, 1972). Thus, there is a natural similarity between creative idea-generating tasks and hard optimization problems (Lovejoy & Sinha, 2010), both of them require efficiently achieving high-quality solutions.
Many optimization problems can be formulated as sequencing (or permutation) problems (Koivisto & Parviainen, 2010; Starkweather et al., 1991). All sequencing problems with 
nodes share the same problem space, in which each potential solution (or state) 
is a permutation {
…, 
} of the integer values from 1 through 
only their objective functions 
possess different structural properties.