Type Alias OpenSingle<T>

OpenSingle: [T] extends [any[]]
    ? OpenSingle<T[number]>[]
    : [T] extends [Algebra.Pattern]
        ? Algebra.Pattern & withMeta
        : [T] extends [Algebra.Expression]
            ? Algebra.Expression
            : [T] extends [Algebra.Operation] ? Operation : T

Maps algebra operation (as union types) Algebra.baseOperations (as interface) as values, staying as precises as possible, and also working on arrays.