let p, q, r be Element of MC-wff ; :: thesis: (q => r) => ((p => q) => (p => r)) in IPC-Taut
A1: (p => (q => r)) => ((p => q) => (p => r)) in IPC-Taut by Def14;
A2: ((q => r) => ((p => (q => r)) => ((p => q) => (p => r)))) => (((q => r) => (p => (q => r))) => ((q => r) => ((p => q) => (p => r)))) in IPC-Taut by Def14;
((p => (q => r)) => ((p => q) => (p => r))) => ((q => r) => ((p => (q => r)) => ((p => q) => (p => r)))) in IPC-Taut by Def14;
then (q => r) => ((p => (q => r)) => ((p => q) => (p => r))) in IPC-Taut by A1, Def14;
then A3: ((q => r) => (p => (q => r))) => ((q => r) => ((p => q) => (p => r))) in IPC-Taut by A2, Def14;
(q => r) => (p => (q => r)) in IPC-Taut by Def14;
hence (q => r) => ((p => q) => (p => r)) in IPC-Taut by A3, Def14; :: thesis: verum