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<p>obtained by the <a href="page.php?w=Rule_of_inference">inference rules</a> of the system applied to the set of axioms.</p>

<p><big> General theories (as expressed in formal language) </big></p>
<p>When defining theories for foundational purposes, additional care must be taken, as normal set-theoretic language may not be appropriate.</p>

<p>The construction of a theory begins by specifying a definite non-empty conceptual class , the elements of which are called statements. These initial statements are often called the primitive elements or elementary</p><p>
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