theorem Th85:
  |-_IPC p => p
proof
A1: |-_IPC p => (p => p) by Th28;
A2: |-_IPC p => ((p => p) => p) by Th28;
    |-_IPC (p => ((p => p) => p)) => ((p => (p => p)) => (p => p))
      by Th29;
    then |-_IPC (p => (p => p)) => (p => p) by A2,Th27;
  hence thesis by A1, Th27;
end;
