Gertrude Stein's first novel, published posthumously as "Things As They Are"

• Letters of proof
• Math initials
• "That's how it's done" mathematically
• Math-proof initials
• Logician's signoff
• Abbr. in a math textbook
• Letters following a proof
• Letters from a mathematician
• Mathematician's "I'm done"

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
QED \Q.E.D\, QED \QED\(k[=u]"[=e]*d[=e]"), interj. [From Latin, quod erat demonstrandum, i.e. which was demonstrated.] Which was demonstrated; -- a phrase used after the conclusion of some line of reasoning, especially in mathematical or logical proofs. ...