Select a HEP event.

def select_event(
    event     = None,
    selection = "ejets"
    ):
    """
    Select a HEP event.
    """
    if selection == "ejets":
        # Require single lepton.
        # Require >= 4 jets.
        if \
            0 < len(event.el_pt) < 2 and \
            len(event.jet_pt) >= 4 and \
            len(event.ljet_m) >= 1:
            return True
        else:
            return False