Konica Hexanon AR 40mm f1.8 is a pancake standard lens, it was shipped as kit lens with Konica SLR cameras during a couple of years in mid and late ’70s. While it is not an actual wide angle lens it is still wider than a normal 50mm lens, which, in my opinion, can be helpful for street photography as it allows to include more of the environment from the same camera to subject distance. It also does so without introducing the perspective distortion of a 35mm wide angle lens with equivalent speed/aperture.
Sometimes it’s hard to explain it but in many situations the 40mm focal length feels just right (i.e. to my taste). When it was introduced some photography magazines considered it the sharpest lens ever produced (for its time that is), there is no hard proofs on that though. You can find it very cheap at about 20-30$. Let’s see if it still is justified to buy this lens today.