transfer, alternation
迭 centers on things taking turns or passing from one to another: transferring a role or alternating in sequence.
迭 combines 辶 (movement) with 失, which likely contributes the sound and the idea of passing or alternating. The exact historical development is uncertain.
The movement radical 辶 wraps around 失 (loss). Picture something being lost and then found again in a cycle: transferring hands and alternating ownership.
For テツ, imagine a transfer of iron (鉄, てつ) goods along a path: 鉄 -> テツ, and the movement radical shows the goods alternating between carriers.
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