Symbolic logic was the basis of the Cybermen's control systems in the Telos Cyber-tombs. It was there to test humans for their intelligence. They would then to be subjected to Cyber-conversion and become the new race of Cybermen.
The controls must have required a genius to solve them as Eric Klieg, a member of the Brotherhood of Logicians, could not work the controls without the Second Doctor. The controls consisted of a series of buttons and levers which had to be pushed and pulled in the correct sequence to operate the Cyber-Technology in the tombs. (TV: The Tomb of the Cybermen)
- It remains unclear whether the Cybermen used symbolic logic purely for testing the intelligence of their "candidates" or if they used it for all their control systems.