reserve SOURCE for non empty finite set,
 p for Probability of Trivial-SigmaField SOURCE,
 Tseq for FinSequence of BoolBinFinTrees IndexedREAL,
 q for FinSequence of NAT;
reserve T for BinHuffmanTree of p;

theorem
 for t,s,r be Element of dom T st t in ( dom T \ (Leaves (dom T)) )
 & s = (t^<* 0 *> ) & r = (t^<* 1 *> ) holds
 Vtree (t) = Vtree (s) + Vtree (r)
proof
A1: ex Tseq,q st Tseq,q,p is_constructingBinHuffmanTree &
 {T} = Tseq.(len Tseq) by Def13;
T in {T} by TARSKI:def 1;
hence thesis by A1,Th21;
end;
