Picard–Lindelöf theorem

The Picard–Lindelöf theorem is like a rule that applies to some kinds of problems that involve numbers. It says that if you start with a certain type of equation (this is the kind of equation that has the same number of things on each side of the equals sign), which has some special properties (like the equation not changing very quickly over time), it will have only one possible solution. That means if you can find the solution to that equation, it's the only one that is true.