El único y su propiedad
Igualada was strongly influenced by Max Stirner. Through his writings he promoted Stirner within Spain, and published the fourth Spanish edition of Stirner's book, "The Ego and Its Own", writing its preface. In 1968 he published a treatise on Stirner, dedicated to the memory of fellow anarchist Émile Armand, and wrote and published the tract, "Anarchism".