RISC JKU 

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Prove

(No contradiction) [Graphics:indexgr395.gif]

with no assumptions.

We prove (No contradiction) by natural deduction.

We prove (No contradiction) by contradiction.

We assume

(No contradiction.pos) [Graphics:indexgr396.gif],

and show [Graphics:indexgr397.gif]

Formula (a contradiction) is proved because (No contradiction.pos.1) and (No contradiction.pos.2) are contradictory.

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