removeResult(ident id, ident studentId, ident sheetId) {
  assume exists //exercises/exercise[id]/students/student[studentId]/result[sheetId]; # implies the existence of pretty much everything
 
  remove //exercises/exercise[id]/students/student[studentId]/result[sheetId];
} # roles: assistant[id], tutor[id, groupId] <- groupId is no parameter of procedure!