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**abhishekkgp** B1) If B is between A and C, (written A*B*C), then A, B, C are three distinct points on a line, and also C*B*A.

B2) For any two distinct points A, B, there exists a point C such that A*B*C

B3) Given three distinct points on a line, one and only one of them is between the other two.

B4) Let A, B, C be three non-collinear points, and let $\displaystyle l$ be a line not containing any of A,B,C. If $\displaystyle l$ contains a point D lying between A and B, then it must also contain either point lying between A and C or a point lying between B and C, but not both.

As for $\displaystyle a+b$, the '+' here is the field addition and $\displaystyle a,b \in F$.