cases_failure.hlean:11:2: error:invalid 'cases' tactic, unification failed
auxiliary goal at time of failure
  A : Type,
  z : A,
  b r t l : z = z,
  s : square t b l r,
  e_3 : z = z
  ⊢ Π (e_4 : eq.rec t (refl z) = idp) (e_5 : eq.rec (eq.rec b (refl z)) e_3 = idp) (e_6 : eq.rec l (refl z) = idp)
    (e_7 : eq.rec (eq.rec r (refl z)) e_3 = idp),
      eq.rec (eq.rec (eq.rec (eq.rec (eq.rec (eq.rec (eq.rec s (refl z)) (refl z)) e_3) e_4) e_5) e_6)
        e_7 = square.ids →
      unit
proof state:
A : Type,
x y z : A,
t : x = y,
b : z = y,
l : x = z,
r : y = y,
s : square t b l r
⊢ unit
cases_failure.hlean:13:0: error: don't know how to synthesize placeholder
A : Type,
x y z : A,
t : x = y,
b : z = y,
l : x = z,
r : y = y,
s : square t b l r
⊢ unit
cases_failure.hlean:13:0: error: failed to add declaration 'foo' to environment, value has metavariables
remark: set 'formatter.hide_full_terms' to false to see the complete term
  ?M_1