▁be ▁difficult ▁to ▁determine ▁whether ▁the ▁license ▁or ▁contract ▁in ▁question ▁is ▁one ▁which ▁the ▁law ▁implies , ▁ir res pective ▁of ▁any ▁protest s ▁by ▁the ▁unw illing ▁lic ensor , ▁or ▁instead ▁one ▁infer red ▁from ▁the ▁whole ▁pattern ▁of ▁fact ual ▁circumstances ▁including ▁the ▁evidence ▁of ▁intent . ▁ ▁In ▁England , ▁there ▁is ▁more ▁of ▁a ▁t endency ▁to ▁regard ▁all ▁imp lied ▁lic enses ▁as ▁matters ▁of ▁fact ▁and ▁intent , ▁while ▁what ▁would ▁be ▁a ▁license ▁imp lied ▁by ▁law ▁in ▁the ▁US ▁is ▁treated ▁under ▁some ▁other ▁branch ▁of ▁substant ive ▁law ▁such ▁as ▁the ▁doctrine ▁of ▁non - der og ation ▁from ▁gr ants . ▁ ▁In ▁both ▁countries , ▁the ▁exhaust ion ▁doctrine ▁has ▁the ▁effect ▁of ▁creating ▁an ▁imp lied ▁license ▁to ▁use ▁a ▁product ▁sold ▁under ▁the ▁" author ity " ▁of ▁the ▁pat ente e . ▁It ▁is ▁controvers ial ▁whether ▁and ▁to ▁what ▁extent ▁contract ual ▁exped ients ▁can ▁successfully ▁limit ▁the ▁scope ▁of ▁such ▁imp lied ▁lic enses . ▁ ▁Express ▁license ▁The ▁opposite ▁of ▁an ▁imp lied ▁license ▁is ▁an ▁express ▁license , ▁which , ▁for ▁some ▁forms ▁of ▁intellectual ▁property , ▁must ▁be ▁in ▁writing . ▁Or al ▁exclusive ▁lic enses ▁were ▁permitted , ▁however , ▁under ▁US ▁copy right ▁law ▁before ▁ 1 9 7 8 . ▁Or al ▁none x clus ive ▁copy right ▁lic enses ▁remain ▁valid ▁under ▁US ▁law . ▁Pat ent ▁lic enses ▁may ▁be ▁or al . ▁Lic enses ▁under ▁the