MacOS – nother way to kill an app other than force quit

If you know the name of the app, you can check in Activity Monitor to see if it's still running there and try its Force Quit. If that doesn't work, take note of the app's process ID (pid). Go to the Terminal and type kill [pid], replacing "[pid]" with the number you noted earlier. If that doesn't work, try kill -3 [pid] and if that doesn't work kill -9 [pid]. If the process is owned by a different user (this is not likely), you may need to replace kill with sudo kill and type your password when prompted.

If the app doesn't show up in Activity Monitor or you couldn't kill it, the window may be a left-over stuck someplace else and the app simply isn't running anymore. In this case, sometimes (not always) it can work to killall SystemUIServer or killall Dock.

If none of this works, you'll have to log out and back in or reboot. The few times I've gotten to this point, the app was so stuck it prevented logging out or shutting down, so I had to hard reboot.

killall kills by process name (which is definitively not 77439 and most probably also not Mathematica). You can use kill 77439 or (if this fails) kill -9 77439 instead (but if the process is really stuck, only a reboot will solve the problem).

Also, due the the way sending/processing of signals (like kill -9) works in Unix/OS X, there are situations where a process will be unkillable. One typical example for this is if a process gets stuck while accessing some external device and never actually gets control back. In such situations a reboot is the only way to get rid of the process.