In Academia SE, there is a question about the credibility of Prof. Richard Duffin, who wrote the notorious letter of recommendation for John Nash, who later received the Nobel Memorial Prize in Economic Sciences. Its answers focus on the credibility of Duffin to the academic/mathematic world. However, since this letter was sent directly to Prof. Solomon Lefschetz, not the adcom, so I have another theory that Duffin had directly credibility to Lefchetz, that is they were friends, or at least know each other personally.
Do you know the relationship between these two professors? I have check their Wikipedia page, but I can't find any evidence.
• Will a recommendation letter such as that written for John F. Nash be convincing? on Academia
• John Forbes Nash, Jr, Richard Duffin, Solomon Lefchetz on Wikipedia
Image taken from the Graduate Alumni Records of Princeton University: