Columbia subject headings:
Dwellings--Energy conservation--Spain--Zaragoza.
Dwellings--Remodeling--Spain--Zaragoza.
Low-income housing--Spain--Zaragoza--History--20th century.
Harvard subject headings:
Dwellings--Energy conservation--Spain--Zaragoza.
Dwellings--Remodeling--Spain--Zaragoza.
Low-income housing--Spain--Zaragoza--History--20th century.
Princeton subject headings: