set a = the HIPERPLANE of V;
set D = { the HIPERPLANE of V};
take { the HIPERPLANE of V} ; :: thesis: for x being set st x in { the HIPERPLANE of V} holds
x is HIPERPLANE of V
thus for x being set st x in { the HIPERPLANE of V} holds
x is HIPERPLANE of V by TARSKI:def 1; :: thesis: verum