He also condemned sedeprivationnism in his recent book (Contra Cekadam) against sedevacantism :
* Canon 160, against sedeprivationnism. "The election of a Sovereign Pontiff is guided solely by "Vacante Sede Apostolica" of Pope Pius X", which constitution, on #29 not only exclude canonical or juridical censures, but also any reason whatsoever to bar a Cardinal from active or passive voice in a Conclave. More on this later.
* Hence it is impossible to find any trace of your sedeprivationism in the legislation of the Church, and cuм Ex has fallen out of use, if it were ever used to bar a Cardinal to the Papacy. Fr GREGORY HESSE explained that cuм Ex was not used, save for its principle (that the holding of an office is incompatible with heresy), because of the regrettable tendency of Paul IV to imprison clerics without trial.
I don't understand Fr. Chazal's condemnation of Sedeprivationism.
First, I don't know why he is bringing up Pius X,
Vacante Sede Apostolica, when the Thesis has nothing to do with the election of the material popes itself (which is considered valid).
Second, I don't know why he is bringing up
cuм Ex at all. Again, the Thesis does not rely on the invalidity of the elections, but on something else. As a matter of fact, in the writings of Fr. Lucien on the Cassisiacuм Thesis, the argument of
cuм Ex is
explicitly set aside as "lacking conclusive force", mainly because of the impracticality of proving the
sin of formal heresy before the conclaves
; and also because
cuм Ex has been abrogated.