I mean, why shouldn't we trust it?<p><i>Assume that R and I are both non-empty sets.<p>By the Axiom of Extensionality, for any two sets X and Y, if X and Y have the same elements, then X=Y. Therefore, if R and I have at least one element in common, then R = I.<p>Now, let r be an element of R and i be an element of I.<p>Since R and I are both non-empty sets, r and i must both exist in either set. Therefore, r = i, and thus R = I.<p>Therefore, the existence of rice pudding and income tax is established. QED.</i>