[FOM] Conservative Extensions of Logic

[F.A.Muller]

Lectori Salutem,

Does anyone know any papers of books where to
find proofs of the following theorem. I am not
100% whether these actually are theorem; I have proofs
of my own about which I am not wholly certain,
which is why I ask: I'd like to compare them with
what is known --- I really have consulted a lot of
logic text-books, but all in vain.

1PL    : classical 1st-order predicate logic
            (no matter how characterised precisely)
1PL+  : 1PL extended with the Frege axioms for
             identity (reflexivity and substitutivity schema)

Thm
1PL+ is a conservative extension of 1PL.

Many thanks in advance,

--> F.A. Muller

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Dr F.A. Muller
Institute for the History & Foundations of Science
Dept. of Physics & Astronomy
Utrecht University
f.a.muller at phys.uu.nl
&
Fac. of Philosophy
Erasmus University Rotterdam
f.a.muller at fwb.eur.nl
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