interface Aircraft { method set_pitch (...); } class Jet : isa Aircraft { method set_pitch (...) {...} } #### class Jet { method set_pitch (...) {...} } interface FlyingThings { require method set_pitch (...); } #### class Piano { method set_pitch (...) {...} } #### ThickInterface ThinInterface \ / ThickThin #### unshift @ThickInterface::ISA, 'ThinInterface';