LaTeX handling of {exercise} directive?

[richard-mevis]

Hello,

i am new to MyST but find it more then suitable for a Website/Book of Exercises/Solutions. The Website works very well with the {exercise} and {solution} ({solution-start}, {solution-end}) directives. But when converting to pdf via LaTeX all these directives (and the {aside} directive) are ignored: "Unhandled LaTeX conversion for node of 'exercise'", as an example error message. I am using the plain_latex_book template.
Is there a tex template that supports my missing directives? If not, is there a way to include some code to the template, which implements the missing directives?

Thanks in advance
richard