# BCS theory and Cooper pairs

I'm studying superconductivity and BCS theory. Looking at the BCS ground state construction, I see two things that seem conflicting

• Occupation of Cooper pairs in BCS ground state (look at the figure below from Ibach)
• The fact that the only electrons in the region $$\pm \Delta$$ about $$E_F$$ contribute to BCS ground state

So where did other electron (electrons not in the $$\pm \Delta$$ region) go?

So where did other electron (electrons not in the $$\pm \Delta$$ region) go?