Related Clues:

• The "E" of 30-Down
• Form of the Latin 'sum'
• Prison (informal)
• “____ erat demonstrandum” may end a mathematical proof
• Was: Lat
• The "E" of 39-Across
• The "E" of Q.E.D
• Jail one of several siblings talked of
• The "E" of Q.E.D
• Q.E.D. center
• "In principio __ Verbum": John 1:1
• The "Q" of QED