© Hillel Wayne 2018
Hillel WaynePractical TLA+https://doi.org/10.1007/978-1-4842-3829-5_1

1. An Example

Hillel Wayne1 
(1)
Chicago, Illinois, USA
 

Let’s write our first specification! In this chapter we will take a simple problem and translate it into a specification. Then, we’ll model check the specification and see if it has a flaw. Spoiler alert, it will have a flaw. This will be a whirlwind tour: we will be using concepts we will gradually learn over the course of the book.

The Problem

Alice and Bob have accounts at Bankgroup. Each account has 0 or more dollars in it. Bankgroup wants to add a new “wire” feature, where any user can transfer money to any other user. This feature has the following requirements:
  • Each wire must be between two different ...

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