Possible Clues:

• Dutch uncle without a notion of geometry
• Geometric theory eccentric uncle maintains
• Cryptic clue by one academic using traditional maths
• Relating to an ancient Greek mathematician
• Learner in audience puzzled about classical geometry
• Grasped by uncle, somehow, concept of ancient geometry
• ____ geometry is about 2,300 years old, and still taught
• Relating to a geometrician of Alexandria c.300BC
• Mathematician's set up hint — left concept on back of publication
• Type of geometry