Furthermore, there must be one and only one thing that would be implied by the parties. For example, in Codelfa Construction Pty Ltd v State Rail Authority of NSW,[18] a term regarding the inability of construction company to work three shifts a day could not be implied because it was unclear what form it would have taken. In English law, this principle was established in the case of Spring v NASDS,[19] in the context of a trade union membership contract.