Columbia subject headings:
Harvard subject headings:
Engelmann, Paul, 1891-1965--Correspondence.
Philosophers--Correspondence.
Wittgenstein, Ludwig, 1889-1951--Correspondence.
Princeton subject headings:
Engelmann, Paul, 1891-1965--Correspondence.
Philosophers--Austria--20th century.
Wittgenstein, Ludwig, 1889-1951--Correspondence.