C# generics type constraint -

should't valid c# code?

class a<t> t : class {      public void dowork<k>() k : t {          var b = new b<k>(); // <- compile time error     } }  class b<u> u : class {  } 

the compiler spits error:

error cs0452: type 'k' must reference type in order use parameter 'u' in generic type or method 'consoleapplication1.b'

shouldn't compiler able figure out k constraint of type t or derived t should reference type (t constrained reference type)?

the constraints applied when type parameter specified. type has not been specified k though k being specified u. u requires type reference type, compiler looking confirm k indeed reference type, cannot. therefore, need explicitly state be.

the specification states in section 4.4.4:

for each clause, type argument corresponds named type parameter checked against each constraint...

and later:

a compile-time error occurs if 1 or more of type parameter’s constraints not satisfied given type arguments.

since type parameters not inherited, constraints never inherited either.

this last point indicates k not inherit constraints t.

update
while conclusions appear correct, evidence little shaky clarified in deleted response eric lippert's response. there, eric stated correct part of specification is:

a type parameter known reference type if has reference type constraint or effective base class not object or system.valuetype.