The ontology of Paul Tillich / by Adrian Thatcher. - Thatcher, Adrian. (OLS)http://pul/name/43600 (Clarendon Press, 1978)
"Bibliography": p. 178-187.

Epistolario 1865-1900 / Friedrich Nietzsche ; a cura di Barbara Allason . - Nietzsche, Friedrich Wilhelm, 1844-1900. (OLS)http://pul/name/664; Allason, Barbara, 1877-1968. (OLS)http://pul/name/14876 (Einaudi, 1969)