A linear space is a set L of objects called points such that, for all P and Q in L and every
real number a, there are
• a unique point P+Q in L called the sum of P and Q and
• a unique point aP in L called the scalar product of a and P
such that the following axioms hold.
[Addition]
1.) P+Q = Q+P for all points P and Q,
2.) P+(Q+R)= (P+Q)+R for all points P,Q and R, and
3.) there is a point 0 such that P+0 = P for every point P.
[Scalar Product] For all points P and Q and all real numbers a and b,
4.) a(P+Q)= aP+aQ,
5.) (a+b)P = aP+bP,
6.) a(bP) = (ab)P and
7.) aP = 0 if and only if a = 0 or P = 0.