for n being non empty Nat
for J being non empty non void Signature
for T being non-empty MSAlgebra over J
for X being V3() GeneratorSet of T
for S1 being non empty non void b₂ -extension b₁ PC-correct QC-correct QCLangSignature over Union X
for L being non-empty Language of X extended_by ({}, the carrier of S1),S1
for G being QC-theory of L
for A being Formula of L
for x, y being Element of Union X st L is vf-qc-correct & L is subst-correct holds
(\ex (x,y,A)) \imp (\ex (y,x,A)) in G