Type inference sometimes fails to resolve aliased type variables

[lionelvillard]

Use case:
type LArguments = PPair<List<Core_cterm_sort> List<Core_cterm_sort>>
func LEnvArgs(LEnv) -> {String:LArguments}

func LEnvGetMetaParams(#env: LEnv, #metavar:String) -> List<Core_cterm_sort>
→ IfPresent(MapGet(LEnvArgs(#env), #metavar), (args)->Fst(args), ()->())