Phragmén–Lindelöf principle
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In complex analysis, the Phragmén–Lindelöf principle (or method), first formulated by Lars Edvard Phragmén (1863–1937) and Ernst Leonard Lindelöf (1870–1946) in 1908, is a technique which employs an auxiliary, parameterized function to prove the boundedness of a holomorphic function (i.e, ) on an unbounded domain when an additional (usually mild) condition constraining the growth of on is given. It is a generalization of the maximum modulus principle, which is only applicable to bounded domains.