changeAttributes(ident uid, ident id, ident groupId, string day, string time, string location, integer maxSize) {
  assume exists /account[uid]/assistant[id];
 
  assume exists /exercise[id]/group[groupId]; # implicitly true in OO implementations
 
  assume maxSize >= 0;
  assume /exercise[id]/group[groupId]/curSize <= maxSize;
 
  update /exercise[id]/group[groupId]/day day;
  update /exercise[id]/group[groupId]/time time;
  update /exercise[id]/group[groupId]/location location;
  update /exercise[id]/group[groupId]/maxSize maxSize;
}