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