theorem Th79:
  |-_IPC p => ((((p => FALSUM) => FALSUM) => FALSUM) => FALSUM)
proof
A1: p => ((p => FALSUM) => FALSUM) in IPC-Taut by Th70,Th72;
  ((p => FALSUM) => FALSUM)=> ((((p => FALSUM) => FALSUM)
  => FALSUM) => FALSUM) in IPC-Taut by Th70,Th72;
  hence thesis by A1,Th69,INTPRO_1:26;
end;
