( ( T
  =
    .   ( next
        =   node stack rhs
          .   !arg:%?node ?stack
            &   whl
              ' ( !node:(?node.?rhs)
                & !rhs !stack:?stack
                )
            & (!node.!stack)
        )
      & !arg:(?stackA,?stackB)
      &   whl
        ' ( !stackA:~
          & !stackB:~
          & next$!stackA:(?leafA.?stackA)
          & next$!stackB:(?leafB.?stackB)
          & !leafA:!leafB
          )
      & out$!arg
      & (   !stackA:!stackB:
          & !leafA:!leafB
          & out$equal
        | out$"not equal"
        )
  )
& T$(x,x)
& T$((x.y),(x.y))
& T$(((x.y).z),(x.y.z))
& T$((x.y.z),(x.y.q))
& T$((x.y),(x.y.q))
& T$((x.y.z),(x.y))
& T$(((x.y).z),(x.z.y))
&   T
  $ ( (a.b.c.(x.y).z)
    , (((a.b).c).x.y.z)
    )
);