626a.lean:3:42: error: don't know how to synthesize placeholder
c : C¹
⊢ ?M_1
626a.lean:3:44: error: don't know how to synthesize placeholder
c : C¹
⊢ Π (a : nat),
    ?M_1 → ?M_1
626a.lean:3:29: error: failed to add declaration 'foo.foo' to environment, value has metavariables
remark: set 'formatter.hide_full_terms' to false to see the complete term
  λ (c : C¹),
    nat.rec_on c ?M_2 ?M_3
626a.lean:8:42: error: don't know how to synthesize placeholder
c : C¹
⊢ ?M_1
626a.lean:8:44: error: don't know how to synthesize placeholder
c : C¹
⊢ Π (a : C¹),
    ?M_1 → ?M_1
626a.lean:8:29: error: failed to add declaration 'boo.foo' to environment, value has metavariables
remark: set 'formatter.hide_full_terms' to false to see the complete term
  λ (c : C¹),
    nat.rec_on c ?M_2 ?M_3