 reserve i,j,n,k,l for Nat;
 reserve T,S,X,Y,Z for Subset of MC-wff;
 reserve p,q,r,t,F,H,G for Element of MC-wff;
 reserve s,U,V for MC-formula;
reserve f,g for FinSequence of [:MC-wff,Proof_Step_Kinds_IPC:];
 reserve X,T for Subset of MC-wff;
 reserve F,G,H,p,q,r,t for Element of MC-wff;
 reserve s,h for MC-formula;
 reserve f for FinSequence of [:MC-wff,Proof_Step_Kinds_IPC:];
 reserve i,j for Element of NAT;
 reserve F1,F2,F3,F4,F5,F6,F7,F8,F9,F10,G for MC-formula;
 reserve x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x for Element of MC-wff;
reserve x1,x2,x3,x4,x5,x6,x7,x8,x9,x10 for object;

theorem Th103:
  |-_IPC (((p => FALSUM) => FALSUM) => FALSUM) => (p => FALSUM)
proof
A1: (p => ((p => FALSUM) => FALSUM)) =>
    ((((p => FALSUM) => FALSUM) => FALSUM) => (p => FALSUM))
    in IPC-Taut by INTPRO_1:24;
  p => ((p => FALSUM) => FALSUM) in IPC-Taut by Th70,Th72;
  then (((p => FALSUM) => FALSUM) => FALSUM) => (p => FALSUM)
    in IPC-Taut by A1,INTPRO_1:def 14;
  hence thesis by Th69;
end;
