Depend is an esolang created by User:PythonshellDebugwindow.
Depend is based around events. Events can have any amount of dependencies, which are other events.
Each line takes the form of a series of two or more strings of alphanumeric characters and underscores. The first two are separated by a dash and greater-than sign, and the rest are separated by commas. Alternatively, a line can be just one such string followed by a dash and greater-than sign.
Each line symbolizes an event whose ID is the line's first string. The rest of the line's strings are that event's dependencies, which are other events (given as IDs). If the event has no dependencies, then it can finish immediately; otherwise, it has to wait until all its dependencies have finished. It is undefined behaviour if an event has itself or an undefined event as a dependency. Empty dependencies (the empty string) are ignored.
? with your input.
0-> 1->2 2->?