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