©1992-2000 Colin Allen. Reproduction by any means strictly prohibited.
The text book says:
identity-intro Conclude any sentence of the form α=α.
Condition: None
Annotation: =I
Assumption set: Empty.

Example.
(a)
1    (1) c=c    =I
Comment. An identity statement of the form α=α, like a theorem, requires no assumptions to justify its assertion.