This man stated that any straight line segment can be extended into a straight line.
This man stated that any straight line segment can be extended into a straight line. When not using his namesake "tools," the straightedge and the compass, he theorized the existence of infinitely many primes. This man stated that, given a straight line and a point, there is only one line passing through the point that never intersects with the line, his Fifth or Parallel Postulate. For 10 points, name this Greek mathematician, the author of Elements and father of pure geometry.
This man stated that any straight line segment can be extended into a straight line.
{Euclid}