Logician's triumphant sign-off

• Geometry abbr
• Calculus class letters
• "That's how it's done"
• The end of mathematics?
• "That's the proof," in math
• ''Proved!'' letters
• Logical letters
• Letters following a proof

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
QED \QED.\ (k[=u]"[=e]*d[=e]"), n. Quantum electrodynamics. [abbrev.]

Wiktionary Word definitions in Wiktionary
alt. quod erat demonstrandum (Latin ''what had to be proved'' or ''what was to be demonstrated''). interj. quod erat demonstrandum (Latin ''what had to be proved'' or ''what was to be demonstrated''). n. quantum electrodynamics.