The shape of Latin S arises from Greek Σ by dropping a single out on the 4 strokes of that letter. The (angular) S-form composed of three strokes existed like a variant of your four-stroke letter Σ currently inside the epigraphy of Western Greek alphabets, plus the 3 and four https://bud-naked-concentrate08531.ampedpages.com/detailed-notes-on-s-58522304