theorem Th25: :: CQC_THE1:29

for Al being QC-alphabet
for X being Subset of (CQC-WFF Al)
for f, g being FinSequence of [:(CQC-WFF Al),Proof_Step_Kinds:] st f is_a_proof_wrt X & g is_a_proof_wrt X holds
f ^ g is_a_proof_wrt X