On the consistency of the \(\Delta_1^1\)-CA fragment of Frege's Grundgesetze
It is well known that Frege's system in the ``Grundgesetze der Arithmetik'' is formally inconsistent. Richard Heck proved that the fragment of Frege's system obtained by restricting the comprehension schema to predicative formulae is consistent and conjectured that the more encompassing \(\Delta_{1}^{1}\)-comprehension schema would already be inconsistent . In the paper under review it is shown that this is not the case.
scientific article; zbMATH DE number 1870147