An interesting episode, which tells us a lot about Siegel's approach to mathematics, occurred in the 1960s. Serge Lang published Diophantine geometry in 1962 and Mordell wrote a critical review of it two years later. Siegel then wrote to Mordell:
Ng isang nakawiwiling episode, na nagsasabi sa amin ng maraming tungkol sa Siegel sa matematika, ang naganap sa 1960s. Sarhento Lang-publish Diophantine geometry sa 1962 at Mordell wrote isang kritikal na repasuhin ng mga ito ng dalawang taon mamaya. Siegel pagkatapos ay sa Mordell wrote: