ible ▁unless ▁" the ▁invol vement ▁of ▁the ▁oppon ent ▁is ▁to ▁be ▁regarded ▁as ▁circum vent ing ▁the ▁law ▁by ▁ab use ▁of ▁process ." ▁ ▁Fil ing ▁of ▁an ▁opposition ▁in ▁common ▁by ▁a ▁group ▁of ▁persons ▁ ▁An ▁opposition ▁may ▁be ▁joint ly ▁file d ▁by ▁more ▁than ▁one ▁natural ▁or ▁legal ▁persons . ▁Such ▁an ▁opposition ▁is ▁adm iss ible ▁upon ▁payment ▁of ▁a ▁single ▁opposition ▁fee . ▁It ▁must , ▁however , ▁be ▁" clear ▁throughout ▁the ▁procedure ▁who ▁belongs ▁to ▁the ▁group ▁of ▁common ▁oppon ents ". ▁ ▁Sub st ant ive ▁exam ination ▁▁ ▁If ▁the ▁opposition ▁is ▁adm iss ible , ▁the ▁grounds ▁for ▁opposition ▁are ▁exam ined ▁as ▁to ▁their ▁mer its . ▁The ▁pat ent ▁propriet or ▁has ▁also ▁the ▁opportunity ▁to ▁reply ▁to ▁the ▁grounds ▁of ▁opposition ▁developed ▁by ▁the ▁oppon ent . ▁Arg uments ▁and , ▁to ▁a ▁certain ▁extent , ▁am end ments ▁may ▁be ▁file d ▁in ▁reply ▁by ▁the ▁pat ent ▁propriet or . ▁ ▁In ▁view ▁of ▁the ▁grounds ▁of ▁opposition , ▁and ▁in ▁view ▁for ▁instance ▁of ▁a ▁prior ▁art ▁document ▁introduced ▁into ▁the ▁proceed ings ▁by ▁the ▁oppon ent , ▁the ▁pat ent ▁propriet or ▁may ▁am end ▁the ▁pat ent , ▁i . e . ▁the ▁description , ▁claims ▁and ▁draw ings ▁of ▁the ▁pat ent , ▁although ▁am end ments ▁may ▁not ▁be ▁file d ▁of ▁right ▁at ▁any ▁stage ▁during ▁the ▁opposition ▁proceed ings . ▁The ▁pat ent ▁propriet or ▁is ▁master