---
⟨1, 0⟩: type_context.is_def_eq trace
  f 0 =?= f a (approximate mode)
    ...failed
---
⟨1, 0⟩: type_context.is_def_eq trace
  f 0 =?= f a (approximate mode)
    f 0 =?= f a
      0 =?= a
      ...failed
    ...failed
---