By studying in steps what a flat plane is, this paper shows that only six axioms are necessary for 2-dimensional Euclidean geometry until the Pythagorean Theorem: 1) the existence of stable space; 2) the existence of a straight line through any two points, 3) the existence of distance measurement between any two points; 4) the limitation of the space to 2-dimensional, 5) the repeated equivalence, and 6) the reflected equivalence.
I also use this to teach kids about math logic and math observation