Merging Either Types in TypeScript's Effect Library

import { Effect, Either } from "effect";

const program = Effect.gen(function* () {
    const a = 5;

    if (a < 5) {
        return Either.right(true);
    } else {
        return Either.left(false);
    }
});
/*
const program: Effect.Effect<Either.Either<boolean, never> | Either.Either<never, boolean>, never, never>
*/