let p, q, r be Element of MC-wff ; :: thesis: (p => (q => r)) => ((p => q) => (p => r)) is valid_IPC
(p => (q => r)) => ((p => q) => (p => r)) in IPC-Taut

proof

IPC-Taut is IPC_theory ;
hence (p => (q => r)) => ((p => q) => (p => r)) in IPC-Taut ; :: thesis: verum

end;

hence (p => (q => r)) => ((p => q) => (p => r)) is valid_IPC ; :: thesis: verum