let p, q, s be Element of MC-wff ; :: thesis: ( p => q in IPC-Taut implies (p 'or' s) => (q 'or' s) in IPC-Taut )
assume A1: p => q in IPC-Taut ; :: thesis: (p 'or' s) => (q 'or' s) in IPC-Taut
(p => q) => ((p 'or' s) => (q 'or' s)) in IPC-Taut by Th60;
hence (p 'or' s) => (q 'or' s) in IPC-Taut by A1, Def14; :: thesis: verum