The Goldbach's conjecture is that $\forall n \in \mathbb{N}^*, \ \exists p,q \in \mathcal{P}$ such that $2n=p+q$.
I wonder if there are some generalization giving more information about the congruence satisfied by $p,q$, for example
Given $m ,a\in \mathbb{N},gcd(a,m)=1$, for every $ n \equiv a \pmod{m}$ large enough, $\exists p,q \in \mathcal{P}$ such that $2n=p+q$ and $p\equiv q \equiv a \pmod{m}$
Is there some reference on this, and is it much harder than the original Goldbach's conjecture ?
The Nature of the Φ(m) Function http://www.vixra.org/abs/1911.0111