1Which punishment or rewards are most effective at maintaining cooperation in public 2 goods interactions and deterring defectors who are willing to freeload on others' 3 contribution? The sanction system is itself a public good and can cause problematic 4 "second-order free riders" who do not contribute to the provisions of the sanctions and thus 5 may subvert the cooperation supported by sanctioning. Recent studies have shown that 6 public goods games with punishment can lead to a coercion-based regime if participation in 7 the game is optional. Here, we reveal that even with compulsory participation, rewards can 8 maintain cooperation within an infinitely large population. We consider three strategies for 9 players in a standard public goods game: to be a cooperator or a defector in a standard 10 public goods game, or to be a rewarder who contributes to the public good and to a fund

Voluntary participation in public goods games (PGGs) has turned out to be a simple but effective mechanism for promoting cooperation under full anonymity. Voluntary participation allows individuals to adopt a risk-aversion strategy, termed loner. A loner refuses to participate in unpromising public enterprises and instead relies on a small but fixed pay-off. This system leads to a cyclic dominance of three pure strategies, cooperators, defectors and loners, but at the same time, there remain two considerable restrictions: the addition of loners cannot stabilize the dynamics and the time average pay-off for each strategy remains equal to the pay-off of loners. Here, we introduce probabilistic participation in PGGs from the standpoint of diversification of risk, namely simple mixed strategies with loners, and prove the existence of a dynamical regime in which the restrictions ono longer hold. Considering two kinds of mixed strategies associated with participants (cooperators or defectors) and non-participants (loners), we can recover all basic evolutionary dynamics of the two strategies: dominance; coexistence; bistability; and neutrality, as special cases depending on pairs of probabilities. Of special interest is that the expected pay-off of each mixed strategy exceeds the pay-off of loners at some interior equilibrium in the coexistence region.

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In 1991, Karl Sims developed a system that enables users to create abstract drawings merely by selecting their favorite images from a computer screen [1]. It was very innovative and great creative impetus to both artists and computer scientists. I was one of computer scientists who planned to implement a similar system to explore the further possibilities of this new technology [2]. I began developing SBART (Simulated Breeding for ART) in 1993 as a successor to Karl Sims's system, with certain unique extensions. Such systems have become recognized as artistic applications of interactive evolutionary computing (IEC) [3]. As in other IEC systems, SBART's main mechanisms are an iteration of visualization, selection by the user and genetic operation. The window, or " eld window," that appears on the screen at the beginning consists of 20 sub-windows, which display individual images of the current population (see Color Plate A No. 3) [4].The following sections describe the distinctive features of SBART 2.4, including genotype representation, multi-eld user interface and facilities for creating collages and short movies.