srecord UndoCreateConcept(long conceptID) implements UndoableWithAnswer {
  transient Concepts cc = db_mainConcepts();
  
  toString { ret "Create " + getConcept(conceptID); }
  
  public S undo() {
    Concept c = getConcept(cc, conceptID);
    S result = "Deleted " + c + " again";
    deleteConcept(conceptID);
    ret result;
  }
}

srecord UndoDeleteConcept(Concept concept) implements UndoableWithAnswer {
  transient Concepts cc = db_mainConcepts();
  
  toString { ret "Delete " + concept; }
  
  public S undo() {
    registerConcept(cc, concept);
    ret "Restored " + concept;
  }
}

srecord UndoSetConceptField(long conceptID, S field, O value, O newValue) implements UndoableWithAnswer {
  transient Concepts cc = db_mainConcepts();
  
  toString { ret "Set " + field + " of " + getConcept(conceptID) + " to " + newValue; }
  
  public S undo() {
    Concept c = getConcept(cc, conceptID);
    S result = "Reset " + field + " of " + c + " to " + value;
    cset(c, field, value);
    ret result;
  }
}