mvarAtDefaultValue.lean:5:7-5:8: error: don't know how to synthesize placeholder
context:
toA : A
x : Nat := toA.x
⊢ Nat
mvarAtDefaultValue.lean:5:2-5:3: error: invalid default value for field 'x', it contains metavariables
  ?m
mvarAtDefaultValue.lean:8:7-8:8: error: don't know how to synthesize placeholder
context:
toA : A
x : Nat := toA.x
⊢ Nat
mvarAtDefaultValue.lean:8:2-8:3: error: invalid default value for field 'x', it contains metavariables
  ?m + 1