let A be QC-alphabet ; :: thesis: for p, q being Element of CQC-WFF A st q in TAUT A holds
p 'or' q in TAUT A
let p, q be Element of CQC-WFF A; :: thesis: ( q in TAUT A implies p 'or' q in TAUT A )
assume A1: q in TAUT A ; :: thesis: p 'or' q in TAUT A
q => (p 'or' q) in TAUT A by Th4;
hence p 'or' q in TAUT A by A1, CQC_THE1:46; :: thesis: verum