The rhyme scheme of to-and-fro is a sort of tonal pattern that Zheng gu and other poets developed for modern "Cstyle poetry in the late Tang Dynasty.

This phenomenon is related to the REEs sources(gyration and discontinuity eruption Emeishan basalt) and the transgression-regression frequently.

When milling and grinding a close plane contour curve on a CNC machine tool, We must select a reasonable curve for the feeding and relieving of the cutter during programming, so as to keep perfect the normal geometric shape at the feeding/relieving point on the contour curve.