"Here intent to deceive may be inferred from findings: (1) that the RFO art was highly material to the prosecution of the ’115 patent, (2) that the applicants knew of the RFO art and knew or should have known of its materiality, and (3) that the patentee has failed to come forward with any credible good faith explanation for the applicants’ failure to disclose prior art use of RFOs to the PTO."

Praxair, Inc. v. ATMI, Inc., 2007-1483 (Fed. Cir., Sept. 29, 2008)
http://www.cafc.uscourts.gov/opinions/07-1483.pdf