altruism

"Ui = U(X, Y, Uj)"

https://www.google.com/search?q=Ui+%3D+U(X%2C+Y%2C+Uj)&rlz=1C1LENP_enUS528US528&oq=Ui+%3D+U(X%2C+Y%2C+Uj)&aqs=chrome.0.57j62.24407j0&sourceid=chrome&ie=UTF-8#rlz=1C1LENP_enUS528US528&sclient=psy-ab&q=%22Ui+%3D+U(X%2C+Y%2C+Uj)%22&oq=%22Ui+%3D+U(X%2C+Y%2C+Uj)%22&gs_l=serp.3...2876.2876.3.3144.1.1.0.0.0.0.112.112.0j1.1.0...0.0.0..1c.1.12.psy-ab.P-5CFsczwqc&pbx=1&bav=on.2,or.r_cp.r_qf.&bvm=bv.47008514,d.aWc&fp=290c805241f20a31&biw=1366&bih=667