Columbia subject headings:
Harvard subject headings:
Porto (Portugal)--Buildings, structures, etc.--Congresses.
Porto (Portugal)--Intellectual life--19th century--Congresses.
Teatro Nacional de S. João (Portugal)--History--19th century--Congresses.
Theater--Portugal--Porto--History--19th century--Congresses.
Theaters--Portugal--Porto--History--19th century--Congresses.
Princeton subject headings:
Porto (Portugal)--Buildings, structures, etc.--Congresses.
Porto (Portugal)--Intellectual life--19th century--Congresses.
Teatro Nacional de S. João (Portugal)--History--19th century--Congresses.
Theater--Portugal--Porto--History--19th century--Congresses.
Theaters--Portugal--Porto--History--19th century--Congresses.