reserve A for QC-alphabet;
reserve sq for FinSequence,
  x,y,z for bound_QC-variable of A,
  p,q,p1,p2,q1 for Element of QC-WFF(A);

theorem Th6:
  p is universal implies p = All(bound_in p, the_scope_of p)
proof
  given x,q such that
A1: p = All(x,q);
A2: p is universal by A1;
  then x = bound_in p by A1,QC_LANG1:def 27;
  hence thesis by A1,A2,QC_LANG1:def 28;
end;
