Hi. Can someone give me a clue on this extra credit problem (I
really need it since I bolloxed up the first quiz) in my
graduate linear algebra course.  Given: V is a vector space such
that whenever v_i is an element of S (for all i=1..n) and such
that the linear combination of those vectors (summation a_i *
v_i) is the zero vector only if all a_i = 0 (in other words, S
is linearly independent).  Prove: Every vector in span(S) can be
uniquely written as a linear combination of S.