Error found:
in module Main
at tests/purs/failing/ClassHeadNoVTA4.purs:8:11 - 8:21 (line 8, column 11 - line 8, column 21)

  No type class instance was found for
                   
    Main.MultiFd 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.useMultiFd
      tyNotAppearInBody

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

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.