Symbolic Logic, D. Jacquette, Wadsworth, 2001, Chpt. 8, IV(13), p.435

The argument:

"All treaties with the Lakota nation are to be honoured. Thus, whatever is not to be honoured is not a treaty with the Lakota nation, and everything is either not a treaty with the Lakota nation or it is to be honoured."

The simplest form of the proof requires no more than working with the definitions as the conclusion is merely a restatement of the premise. Contraposition and material implication have been used.

1. (x)(Txl ⊃Hx)
2. ∴ (x)(¬ Hx ⊃¬ Txl) • (x)(¬ Txl ∨Hx)
3. (x)(¬ Hx ⊃¬ Txl) ......... 1 Contrap.
4. (x)(¬ Txl ∨Hx) ......... 1 MI
5. (x)(¬ Hx ⊃¬ Txl) • (x)(¬ Txl ∨Hx) ......... 3,4 Conj.