Some Properties Of The Sorgenfrey Line And The Sorgenfrey Plane

We first provide a modified version of the proof in [3] that the Sorgenfrey line is T-1. Here, we prove that it is in fact T-2, a stronger result. Next, we prove that all subspaces of R-1 (that is the real line with the usual topology) are Lindelof. We utilize this result in the proof that the Sorgenfrey line is Lindelof, which is based on the proof found in [8]. Next, we construct the Sorgenfrey plane, as the product topology of the Sorgenfrey line and itself. We prove that the Sorgenfrey plane is not Lindelof, and therefore the product space of two Lindelof spaces need not be Lindelof. Further, we note that the Sorgenfrey line is regular, following from [3]:59. Next, we observe that the Sorgenfrey line is normal since it is both regular and Lindelof. Finally, we prove that the Sorgenfrey plane is not normal, and hence the product of two normal spaces need not be normal. The proof that the Sorgenfrey plane is not normal and many of the lemmas leading up to this result are modelled after the proof in [3], that the Niemytzki plane is not normal. Information was also gathered from [15].