BUG: Combinator tree is wrong for Dyadic separators

[tom-huntington]

I was trying to add the output of two trees using dyadic separators (i.e. two dyadic trees feeding into Φ₁), but noticed a bug.

Here's a minimal reproducible example. l is a stand in for the left tree, r for the right tree. The answer should be Φ₁, but Jello is giving BB. The BB is the right answer in the monadic case m-m-m (i.e. a 1-1-1 chain).

> 1 2 :: l : + : r
         ḷ ð + ð ṛ
   ḷ     1 2 ➡️  1
   ḷð+   1 2 ➡️  1
   ḷð+ðṛ 1 2 ➡️  3
    This is a 2-s-2-s-2 dyadic chain (dBB)
              │   │   │
              d   d   d
              └─┬─┘   ⋮
                B     ⋮
                └──┬──┘
                   B

[codereport]

You are definitely correct about this. Will plan to fix at some point.