The footnotes refer to these editions.

Ayn Rand, Philosophy: Who Needs It, Signet, Penguin Books, 1984

Ayn Rand, The Virtue of Selfishness, Signet, New American Library, 1964

Ayn Rand, For the New Intellectual, Signet, New American Library, 1961

Ayn Rand, Capitalism: the Unknown Ideal, Signet, New American Library, 1962

Ayn Rand, Introduction to Objectivist Epistemology, Mentor, New American Library, 1979

Ayn Rand, Atlas Shrugged, Signet, Penguin Group, 1957

S. I. Hayakawa, Language in Thought and Action, Harvest Edition, Harcourt, Brace & Company, 1992

There are also various links to on-line references in several posts.