https://s0.wp.com/latex.php?latex=u%28t%29%5Cleft%5C%7B%5Cbegin%7Bmatrix%7D++0%26t%3C0+%5C%5C++A+%260%5Cleq+t+%5Cleq+b%5C%5C++0+%26+t%3Eb++%5Cend%7Bmatrix%7D%5Cright.&bg=ffffff&fg=000000&s=0