let V be RealLinearSpace; :: thesis: for v being VECTOR of V
for l being Linear_Combination of {v} holds Sum l = (l . v) * v
let v be VECTOR of V; :: thesis: for l being Linear_Combination of {v} holds Sum l = (l . v) * v
let l be Linear_Combination of {v}; :: thesis: Sum l = (l . v) * v
A1: Carrier l c= {v} by Def6;

now :: thesis: Sum l = (l . v) * v

per cases ( Carrier l = {} or Carrier l = {v} ) by A1, ZFMISC_1:33;

suppose Carrier l = {} ; :: thesis: Sum l = (l . v) * v

then A2: l = ZeroLC V by Def5;
hence Sum l = 0. V by Lm2
.= 0 * v by RLVECT_1:10
.= (l . v) * v by A2, Th20 ;
:: thesis: verum

end;

suppose Carrier l = {v} ; :: thesis: Sum l = (l . v) * v

then consider F being FinSequence of V such that
A3: ( F is one-to-one & rng F = {v} ) and
A4: Sum l = Sum (l (#) F) by Def8;
F = <*v*> by A3, FINSEQ_3:97;
then l (#) F = <*((l . v) * v)*> by Th26;
hence Sum l = (l . v) * v by A4, RLVECT_1:44; :: thesis: verum

end;

end;

end;

hence Sum l = (l . v) * v ; :: thesis: verum