For example: premise A→B, B→C, conclusion A → C.
Prove:
(1) A P (annex)
(2) A → B
B T( 1)(2)I
(4)B→C P
(5) Item 1, Paragraph 4, Article 3 of the Council of Europe Treaty.
(6)A→C CP
When proved by the reduction to absurdity.
Premise a, A→B, conclusion b
Prove:
(1)┐B P (annex)
(2) A → B
(3)┐B→┐A T(2)E
(4)┐A T( 1)(3)I
(5) a PI
(6) A contradiction of ∧ ┐A T(4)(5)