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deleteGroup(ident id, ident groupId) {
assume exists //exercises/exercise[id]/groups/group[groupId];
assume size(//accounts/account/tutor[id]/group[groupId]) = 0;
assume count(groupId, //exercises/exercise[id]/students/student/group)) = 0;
remove //exercises/exercise[id]/groups/group[id];
} # roles: assistant[id]