Early morning riddle

Morning folks. An early morning riddle for you:
What 'e' has a method, a problem and a relation?

Natural logarithm?

It is Euler.

method: A method for approximating function in differential equations.
problem: 2 fixed centers problem related to gravity and movement in the cartesian plane.
relation: e^(i*pi)+1=0.

actually it could also be euclid, but you are probably thinking of euler.

euclid:
Method: Eucliding method for prime factorization
Problem: Euclid's 47th problem is pretty famous, it is the same as the Pythagorean theorm, but Euclid was the first to publish it
Relation: In any map on a sphere, the number of countries plus the number of vertices exceeds the number edges by 2

Give that man a prize! :D

Well done galway, right first time. I meant his Bridges of Konisberg (spelling?) problem but hey, the right answer is the right answer.

Haven't seen you around here before. Welcome on board.