theorem
  {F1,F2,F3,F4,F5,F6,F7,F8,F9} |-_IPC G implies
  {F2,F3,F4,F5,F6,F7,F8,F9} |-_IPC F1 => G
proof
  {F1,F2,F3,F4,F5,F6,F7,F8,F9} =
    {F2,F3,F4,F5,F6,F7, F8,F9} \/ {F1} by ENUMSET1:77;
  hence thesis by Th53;
end;
