CS304: Relational Algebra: bi-coastal

π_Name(Contacts⋈_ID=ID(σ_State=CA(Address) ⋈_ID=ID σ_State=MA(Address)))

Or:

π_Name(Contacts⋈_ID=ID(π_id(σ_State=CA(Address)) ∩ π_id(σ_State=MA(Address))))

Or, using renaming:

π_Name(σ_{State=CA AND State2=MA}(Contacts ⋈ Address ⋈_ID=ID Address[ID,State2]))