trait PaymentableMapper[OwnerType <: PaymentableMapper[OwnerType]]
    extends LongKeyedMapper[OwnerType] {
    self: OwnerType =>
    def paid: Unit
}

trait PaymentableMetaMapper[OwnerType <: PaymentableMapper[OwnerType]]
    extends LongKeyedMetaMapper[OwnerType] {
    self: OwnerType =>
}

abstract class MappedPaymentable[T <: Mapper[T], P <: PaymentableMetaMapper[_]]
    (owner: T, paymentable: => P) extends MappedLongForeignKey(owner, paymentable)

ERROR:
[info] Compiling main sources...
[error] /.../.../PaymentableMapper.scala:14: no type parameters for constructor MappedLongForeignKey: (theOwner: T,_foreignMeta: => net.liftweb.mapper.KeyedMetaMapper[Long,O])net.liftweb.mapper.MappedLongForeignKey[T,O] exist so that it can be applied to arguments (T, P)
[error]  --- because ---
[error] argument expression's type is not compatible with formal parameter type;
[error]  found   : P
[error]  required: net.liftweb.mapper.KeyedMetaMapper[Long,?O]
[error] abstract class MappedPaymentable[T <: Mapper[T], P <: PaymentableMetaMapper[_]](owner: T, paymentable: => P)
[error]                                                                                ^
[error] one error found