let p, q, s be Element of MC-wff ; :: thesis: (p => q) => (p => (q 'or' s)) in IPC-Taut
A1: (q => (q 'or' s)) => ((p => q) => (p => (q 'or' s))) in IPC-Taut by Th22;
q => (q 'or' s) in IPC-Taut by Def14;
hence (p => q) => (p => (q 'or' s)) in IPC-Taut by A1, Def14; :: thesis: verum