P filed an action in the District of Massachusetts against Ds to recover on promissory notes relating to a sale of stock in Winnipesaukee Airlines, Inc., by P to Ds. P's complaint alleged federal jurisdiction on the basis of diversity of citizenship under 28 U.S.C. § 1332. The complaint did not allege citizenship but did state that P resided in Arlington, Massachusetts. Ds filed a motion to dismiss for lack of subject matter jurisdiction on the ground that complete diversity of citizenship did not exist. The motion, which included affidavits and other evidentiary documents, alleged that P, as well as Ds, were citizens of New Hampshire. P filed an objection to the motion to dismiss, including affidavits, in which he alleged that he was a citizen of Florida. P asked that the district court permit him to amend his complaint to assert Florida citizenship. Under 28 U.S.C. § 1332(a)(1), there is diversity of citizenship if the plaintiff is a 'citizen' of a different state than all of the defendants. 'Citizenship' in a state is the equivalent of 'domicile.' Where a party changes domicile, 'domicile at the time suit is filed is the test and jurisdiction once established is not lost by a subsequent change in citizenship.' The burden of proof is on the plaintiff to support allegations of jurisdiction with competent proof when the allegations are challenged by the defendant. Ds presented evidence that P was a New Hampshire citizen: (1) P owned real property in Melvin Village, New Hampshire and paid taxes on that property; (2) P maintained a functioning telephone in Melvin Village; (3) P had had a New Hampshire driver's license since 1986; (4) P was registered to vote in New Hampshire from 1976 until at least 1990, and has actually voted in New Hampshire during that time; and (5) P or P's wife stated his address to be in Melvin Village, New Hampshire on 1986, 1987, and 1988 annual reports filed with the New Hampshire Secretary of State by Amphibair, Inc., a corporation of which P was sole director, President, and Treasurer, and P's wife was Secretary. P presented affidavits of himself and his wife setting forth primarily the following evidence that P was a citizen of Florida: (1) P purchased real property in Florida and moved there in 1984, keeping his New Hampshire property as a summer home; (2) that since 1984 P has maintained several Florida bank accounts; (3) that P has a Florida driver's license; (4) that P's wife has run a horse farm continuously in Florida since 1984; (5) that P and/or his wife belong to several social organizations in Florida; (6) that P has summered in New Hampshire, in some years spending as little as two to three weeks there; (7) that all of P's personal belongings are in Florida except for certain bank accounts and sparse furnishings in the Melvin Village, New Hampshire residence; and (8) that P listed a Florida residence on his federal tax returns for 1987, 1988, and 1989. The court placed weight on P's voter registration in New Hampshire and on P's representations of New Hampshire residence on corporate filings. The court granted the motion of Ds finding a lack of complete diversity of citizenship. P appealed.