"That's how it's done"

• Letters at the end of a math dissertation, perhaps
• Proof-ending abbr
• Abbr. after a series of equations, maybe
• Geometry proof letters
• "Proven," in proofs
• Logician's letters
• Ending letters
• Conclusive letters

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.

Wikipedia Word definitions in Wikipedia
QED were an Australian New Wave trio, whose lead singer, Jenny Morris , went on to achieve commercial success as a solo artist. The band had a top twenty hit single, "Everywhere I Go", on the Australian Kent Music Report in 1983.