reconsider A = y=0-line as Subset of Niemytzki-plane by Def3, Th19;
Int (Cl A) = Int A by Th26, PRE_TOPC:22
.= {} by Th35 ;
hence y=0-line is nowhere_dense Subset of Niemytzki-plane by TOPS_3:def 3; :: thesis: verum