def is_in(x, l):
    """Transforms into set and checks existence

    Given an element `x` and an array-like `l`, this function turns `l` into a
    set and checks the existence of `x` in `l`.

    Parameters
    --------
    x : any
    l : array-like

    Returns
    --------
    bool

    """
    return x in set(l)