This time we are using the descriptive mode of C.a.R. This mode can be used in files to describe complete constructions including macro definitions. Or it can be used interactively in applets or the application, as in this example. It is also used to access the applet from a web page with JavaScript.
The above assignment is to construct the circle through the three points. You have the tools: circle, intersection and a macro called "MP", which constructs the reflection line between two points. For the syntax of possible commands see here.