[NTG-context] Place for exercises and solutions

Dear Sirs, I'm writing a chemical book and I want include some exercises in the end of each chapter. In the source file the solutions are placed after the related exercise. In the .pdf file the exercises should be located at end of each chapter, but the solutions should appear in the end of the book. Did anybody has a similar implementation? Thanks a lot Jorge Magalhães Abraços, Jorge Manuel de Almeida Magalhães