The superconducting gap is a fundamental characteristic of superconductors, representing an energy range around the Fermi level where no electronic states can exist. It signifies the energy required to break a Cooper pair (a bound state of two electrons with opposite momenta and spins) and create two quasi-particles. Peper by discusses this phenomenon. The authors begin with experimental motivation, observing an enhanced superconducting gap near impurities compared to the clean-bulk value. To explore this, they performed simulations using the Bogoliubov-de Gennes theory applied to the attractive Hubbard model, which qualitatively reproduced the enhancement. This effect is attributed to an increased local density of states at the Fermi energy near impurity sites. Additionally, the simulations revealed significant differences between thin (2D) and thick (3D) films, with pronounced Friedel oscillations in 2D decaying much faster in 3D, aligning qualitatively with experiments.