theorem Th116: :: Restricted cut rule, No.2
  (X |-_IPC r) & (X \/ {r} |-_IPC q) implies X |-_IPC q
proof
  assume A1: (X |-_IPC r) & (X \/ {r} |-_IPC q); then
  X |-_IPC r => q by Th53;
  hence thesis by A1,Th27;
end;
