let p, q be Element of MC-wff ; :: thesis: q => (p 'or' q) is valid_IPC
q => (p 'or' q) in IPC-Taut

proof

IPC-Taut is IPC_theory ;
hence q => (p 'or' q) in IPC-Taut ; :: thesis: verum

end;

hence q => (p 'or' q) is valid_IPC ; :: thesis: verum