|Description: Principle of identity.
Theorem *2.08 of [WhiteheadRussell] p.
version is proved directly from the axioms for demonstration purposes.
This proof is a popular example in the literature and is identical, step
for step, to the proofs of Theorem 1 of [Margaris] p. 51, Example 2.7(a)
of [Hamilton] p. 31, Lemma 10.3 of [BellMachover] p. 36, and Lemma 1.8 of
[Mendelson] p. 36. It is also "Our
first proof" in Hirst and Hirst's A
Primer for Logic and Proof p. 17 (PDF p. 23) at
shorter version of the proof that takes advantage of previously proved
theorems, see id 19. (Contributed by NM, 5-Aug-1993.)
(New usage is discouraged.) (Proof modification is