S NO FURTHER A MYSTERY

The form of Latin S arises from Greek Σ by dropping just one out from the 4 strokes of that letter. The (angular) S-form made up of three strokes existed being a variant of the four-stroke letter Σ by now inside the epigraphy of Western Greek alphabets, as well as the 3 and 4 strokes variants existed alongside one another while in the classical E