Evidence shows that even state and local handgun control laws work. For example, in $\mathrm{1974}$ Massachusetts passed the Bartly$-$Fox Law, which requires a special license to carry a handgun outside the home or business. The law is supported by a mandatory prison sentence. Studies by Glenn Pierce and William Bowers of Northeastern University documented that after the law was passed handgun homicides in Massachusetts fell $\mathrm{50}\%$ and the number of armed robberies dropped $\mathrm{35}\%$ this are examples of$?$