A certain critical two-soliton solution of the nonlinear Schr?dinger equation
A certain critical two-soliton solution of the nonlinear Schroedinger equation

An exact two-soliton solution of the nonlinear Schr?dinger equation is derived by using the Hirota direct approach. This solution describes such a critical process that two still solitons separated infinitely approach and then pass through each other and keep straight on infinitely.