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<p>were being founded. <a href="page.php?w=Jan_Lukasiewicz">Jan Lukasiewicz</a>  suggested in 1926 that one could improve on <a href="page.php?w=Hilbert_system">Hilbert system</a>s as a basis for the axiomatic presentation of logic if one allowed the drawing of conclusions from assumptions in the inference rules of the logic.  In response to this, <a href="page.php?w=Stanislaw_Jaskowski">Stanislaw Jaskowski</a> (1929) and <a href="page.php?w=Gerhard_Gentzen">Gerhard Gentzen</a> (1934) independently provided such systems, called calculi of <a href="page.php?w=natural_deduction">natural deduction</a>,</p><p>
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