let X be Subset of MC-wff; :: thesis: for p, q being Element of MC-wff holds q => (p 'or' q) in CnIPC X
let p, q be Element of MC-wff ; :: thesis: q => (p 'or' q) in CnIPC X
for T being Subset of MC-wff st T is IPC_theory & X c= T holds
q => (p 'or' q) in T ;
hence q => (p 'or' q) in CnIPC X by Def15; :: thesis: verum