type alias L.Unionizeimport { type L } from "https://deno.land/x/ts_toolbelt_unofficial@1.1.0/mod.ts"; const { Unionize } = L; Make the fields of L union the ones of L1 ExamplesExample 1 Type ParametersL extends ListL1 extends ListoptionalK extends Key = Keydefinition: [P in keyof L]: P extends K ? L[P] | At<L1, P> : L[P]