@value interface Type<#a, #b|#c, #d|#e, #f> {
  refines Parent
  refines Other<Type2<#a>, #f>

  get () -> (#x)
  set (#x) -> ()

  something<#y>
    #y requires T1
    #y allows T2
    #y defines T3
  (#y) -> (#y)
}