theorem Th92:
  |-_IPC (q => (p => FALSUM)) 'equiv' ((p '&' q) => FALSUM)
proof
A1: |-_IPC ((p '&' q) => FALSUM) => (q => (p => FALSUM)) by Th90;
  |-_IPC (q => (p => FALSUM)) => ((p '&' q) => FALSUM) by Th91;
  hence thesis by A1,Th84;
end;
