Street demonstrations occur across the world. In Rio de Janeiro, in June/July 2013, they reach beyond one million people. A wrathful reader of O Globo, a leading newspaper in the same city, published a letter (Ferreira (2011)  [10]) where many social questions are stated and answered Yes or No....

In this work we study the problem of tax evasion on a fully-connected population. For this purpose, we consider that the agents may be in three different states, namely honest tax payers, tax evaders and undecided, that are individuals in an intermediate class among honests and evaders. Every...