In the softened version of the singular isothermal sphere model, the dimensionless potential named for this phenomenon is modified to equal the square root of the expression “position squared plus core radius squared,” thereby avoiding a singularity. The foundation for the modern theory of this phenomenon rests on a pair of 1964 papers by Sjur (“shoor”) Refsdal. The Jacobian matrix that describes the change of coordinates (10[1])induced by this phenomenon can be decomposed into a convergence term and a shear term. (10[1])This phenomenon perturbs the line element of the Schwarzschild (“shwartz-shilled”) metric by a factor of “two times (10[1]-5[1])the Newtonian potential over c-squared.” Observing (-5[1])the weak form of this phenomenon (10[2])requires analyzing many slightly distorted (10[1])images, (10[3])while its (10[2])strong (10[1])form creates (10[1])easily visible distortions, such as an Einstein ring. (10[4])For 10 points, (10[1])name this phenomenon in which matter bends light. (10[1]0[1])■END■