Possible Clues:

• Teacher at Alexandria
• Helpful sign written the wrong way by top mathematician
• Greek mathematician, 3rd century BC
• Who wrote to Ptolemy I 'There is no royal road to geometry'
• 'The Father of Geometry'
• Sign reversed by top Greek mathematician ...
• Rising, tip hat as old mathematician appears
• Master of lengths and angles put cue back with cover on
• Old Greek geometrician
• The "Father of Geometry"