
theorem Th21:
  for n be Nat for x,y being FinSequence holds
  (n+1)-BitGFA1Str(x, y) = n-BitGFA1Str(x, y) +*
  BitGFA1Str(x .(n+1), y.(n+1), n-BitGFA1CarryOutput(x, y)) &
  (n+1)-BitGFA1Circ(x, y) = n-BitGFA1Circ(x, y) +*
  BitGFA1Circ(x .(n+1), y.(n+1), n-BitGFA1CarryOutput(x, y)) &
  (n+1)-BitGFA1CarryOutput(x, y) =
  GFA1CarryOutput(x .(n+1), y.(n+1), n-BitGFA1CarryOutput(x, y))
proof
  set f0 = 1GateCircStr(<*>,(0-tuples_on BOOLEAN)-->TRUE);
  set g0 = 1GateCircuit(<*>,(0-tuples_on BOOLEAN)-->TRUE);
  set h0 = [<*>, (0-tuples_on BOOLEAN)-->TRUE];
  let n be Nat;
  let x,y be FinSequence;
  consider f,g,h being ManySortedSet of NAT such that
A1: n-BitGFA1Str(x,y) = f.n and
A2: n-BitGFA1Circ(x,y) = g.n and
A3: f.0 = f0 and
A4: g.0 = g0 and
A5: h.0 = h0 and
A6: for n being Nat, S being non empty ManySortedSign,
  A being non-empty MSAlgebra over S
  for z be set st S = f.n & A = g.n & z = h.n holds
  f.(n+1) = S +* BitGFA1Str(x .(n+1), y.(n+1), z) &
  g.(n+1) = A +* BitGFA1Circ(x .(n+1), y.(n+1), z) &
  h.(n+1) = GFA1CarryOutput(x .(n+1), y.(n+1), z) by Def6;
A7: n-BitGFA1CarryOutput(x, y) = h.n by A3,A4,A5,A6,Th15;
A8: (n+1)-BitGFA1Str(x, y) = f.(n+1) by A3,A4,A5,A6,Th15;
A9: (n+1)-BitGFA1Circ(x, y) = g.(n+1) by A3,A4,A5,A6,Th15;
  (n+1)-BitGFA1CarryOutput(x, y) = h.(n+1) by A3,A4,A5,A6,Th15;
  hence thesis by A1,A2,A6,A7,A8,A9;
end;
