A1: { (l . j) where j is Nat : ( 1 <= j & j <= len l & l . j in fixed_QC-variables A ) } = {} by Th5;
{ (l . i) where i is Nat : ( 1 <= i & i <= len l & l . i in free_QC-variables A ) } = {} by Th5;
hence P ! l is Element of CQC-WFF A by A1, Th7; :: thesis: verum