Sum.someRight.{u_1, 0} (α := ?m) (c (α := ?m) : Sum ?m Nat) : Option Nat
evalWithMVar.lean:13:6-13:21: error: don't know how to synthesize implicit argument
  @Sum.someRight.{?u, 0} ?m Nat (c (α := ?m) : Sum ?m Nat)
context:
⊢ Type ?u
evalWithMVar.lean:13:20-13:21: error: don't know how to synthesize implicit argument
  @c ?m
context:
⊢ Type ?u
Sum.someRight.{u_1, 0} (α := ?m) (c (α := ?m) : Sum ?m Nat) : Option Nat
Sum.someRight.{u_1, 0} (α := ?m) (c (α := ?m) : Sum ?m Nat) : Option Nat