reserve A for QC-alphabet;
reserve p, q, r, s, p1, q1 for Element of CQC-WFF(A),
  X, Y, Z, X1, X2 for Subset of CQC-WFF(A),
  h for QC-formula of A,
  x, y for bound_QC-variable of A,
  n for Element of NAT;

theorem Th10:
  X |- {p} iff X |- p
proof
  hereby
    p in {p} by TARSKI:def 1;
    hence X |- {p} implies X |- p;
  end;
  thus thesis by TARSKI:def 1;
end;
