I have a Fighter with twf, itwf, greater trip and hammer the gap.
I have two questions about that:
1: 'hiting' the trip counts as a 'hit' for Hammer the gap?
2: if in my Full Attack Action I make the trip in my first attack, then the 
  opponent generates an AoO (for Greater Trip), if I hit this attack of opportunity it would count towards the 
  Hammer the Gap bonus?