Appeal No. 2005-0841
Application No. 08/230,083
determining whether a patentee has overcome the Warner-
Jenkinson presumption, so as not to undermine the
public notice function served by that record). If the
patentee successfully establishes that the amendment
was not for a reason of patentability, then prosecution
history estoppel does not apply.
***
. . . By its very nature, objective unforeseeability
depends on underlying factual issues relating to, for
example, the state of the art and the understanding of
a hypothetical person of ordinary skill in the art at
the time of the amendment. Therefore, in determining
whether an alleged equivalent would have been
unforeseeable, a district court may hear expert
testimony and consider other extrinsic evidence
relating to the relevant factual inquiries.
. . . As we have held in the Warner-Jenkinson
context, that reason should be discernible from the
prosecution history record, if the public notice
function of a patent and its prosecution history is to
have significance. See id. at 1356 ("Only the public
record of the patent prosecution, the prosecution
history, can be a basis for [the reason for the
amendment to the claim]. Otherwise, the public notice
function of the patent record would be undermined.");
Festo [I], 234 F.3d at 586 ("In order to give due
deference to public notice considerations under the
Warner-Jenkinson framework, a patent holder seeking to
establish the reason for an amendment must base his
arguments solely upon the public record of the patent’s
prosecution, i.e., the patent's prosecution history.
To hold otherwise--that is, to allow a patent holder to
rely on evidence not in the public record to establish
a reason for an amendment--would undermine the public
notice function of the patent record."). Moreover,
whether an amendment was merely tangential to an
alleged equivalent necessarily requires focus on the
context in which the amendment was made; hence the
resort to the prosecution history. Thus, whether the
patentee has established a merely tangential reason for
a narrowing amendment is for the court to determine
from the prosecution history record without the
introduction of additional evidence, except, when
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