In the underlying وَوَاصِلُ, the book changes the first wāw to hamzah, yielding أَوَاصِلُ. The second wāw remains.
UnderlyingResultChanged letter
وَوَاصِلُأَوَاصِلُFirst wāw
وَوَاعِدُأَوَاعِدُFirst wāw
The operation is neither the deletion of both wāws nor replacement of the second one. A good morphological explanation identifies the exact position of the changed letter.
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Miscellaneous Morphological Explanations: Eight Rules for Wāw, Yāʾ, Alif and Hamzah
In the underlying وَوَاصِلُ, the book changes the first wāw to hamzah, yielding أَوَاصِلُ. The second wāw remains.
UnderlyingResultChanged letter
وَوَاصِلُأَوَاصِلُFirst wāw
وَوَاعِدُأَوَاعِدُFirst wāw
The operation is neither the deletion of both wāws nor replacement of the second one. A good morphological explanation identifies the exact position of the changed letter.