Constellation Schema; Relationships between fact tables What are acceptable types of depedendcies between facts in a multiple-fact schema?

Conceptually talking, As you know a Multi-Dimensional Model may have multiple facts (like in a constellation schema).

Now my question is: if we have for example two facts in the schema and those two facts have a relationship between them. 

1- Is having a relationship between the two facts acceptable from a theoretical point of view?

2- If it's acceptable; what is these kinds of the available relationships?

fact1 (1-1) fact2 ;
fact1 (1-n) fact2 ;
fact1 (n-1) fact2 ;
fact1 (n-n) fact2  ;

3- Do the measures have a role in identifying these acceptable relationships. I read that having a (1-n) is acceptable when the measures are in the n side!

Are there any references?
Not really. Fact tables has rows which are a intersection of all the joined dimensions. Joining a fact table to another fact table doesn't really make sense - two facts should be joined through a conformed dimension.
I don't consider it acceptable.
No. Measures quantify the intersection of all the dimensions, they enable you to measure that item not change the granularity or definition of that item. That is what Dimension tables are for.