Original hamzah stays; feminine hamzah becomes wāw; hamzah substituting for wāw/yāʾ permits both retaining hamzah and replacing it with wāw.
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Three Hamzah Conditions
The Dual Noun: Inflection, Maqṣūr, Mamdūd and Iḍāfah
Original hamzah stays; feminine hamzah becomes wāw; hamzah substituting for wāw/yāʾ permits both retaining hamzah and replacing it with wāw.