A formal presentation of the language can be found in the 1991 Proceedings of the IEEE.
[1] In 1993 it progressed to practical, industrial use in a commercial product as the core language of the industrial environment SCADE, developed by Esterel Technologies.
It is now used for critical control software in aircraft,[2] helicopters, and nuclear power plants.
In this example the node foo returns the negation of its input a, which is the expected result.
Additional internal variables can be declared as follows: Note: The equations order doesn't matter, the order of lines U = X and Y; and Z = not U; doesn't change the result.