Will substitutes; inter vivos trust

[Under the "probate exception" to federal jurisdiction, federal courts sometimes decline to hear cases that are essentially disputes over property referenced in a will and controlled by a state probate court.  In the excerpt quoted below, a court observed that due to the similarity between wills and will substitutes, the probate exception might apply even in the presence of a legal instrument that was not technically a will.]

"The plaintiffs argue that the probate exception is inapplicable here because this action relates to the execution of an inter vivos trust, not to a will.  We reject such a per se rule.  The inter vivos trust is clearly a will substitute.  However, the fact that this case [involves] a will substitute does not automatically render the probate exception applicable."