Error found:
in module Main
at tests/purs/failing/ClassHeadNoVTA2.purs:10:9 - 10:17 (line 10, column 9 - line 10, column 17)

  No type class instance was found for
                 
    Main.Multi t0
               t1
                 
  The instance head contains unknown type variables.

  Note: The following type class members found in the expression require visible type applications to be unambiguous (e.g. tyClassMember @Int).
    Main.useMulti
      tyNotAppearInBody, norThisOne

while checking that type forall (t20 :: Type) (t21 :: Type) (@tyNotAppearInBody :: t20) (@norThisOne :: t21). Multi @t20 @t21 tyNotAppearInBody norThisOne => Int
  is at least as general as type Int
while checking that expression useMulti
  has type Int
in value declaration multi

where t0 is an unknown type
      t1 is an unknown type

See https://github.com/purescript/documentation/blob/master/errors/NoInstanceFound.md for more information,
or to contribute content related to this error.