convert bridi into n-ary property claim: xn is such that it fills the n-th occurrence of ce'u in [bridi].
Similar to poi'i but using ce'u instead of ke'a as the binding variable, thus allowing for plural properties. In particular, allows for an alternative way of defining brivla. E.g. cabna = "ka'oi'i ce'u fasnu ca ce'u kei". See also ka, poi'i, ce'u.