let p, q, s be Element of MC-wff ; :: thesis: ((p '&' q) '&' s) => q in IPC-Taut
A1: (p '&' q) => q in IPC-Taut by Def14;
((p '&' q) '&' s) => (p '&' q) in IPC-Taut by Def14;
hence ((p '&' q) '&' s) => q in IPC-Taut by A1, Th26; :: thesis: verum