interactInertExp :: [Xi] -> Xi -> [Xi] -> Xi -> [Pair Type]
interactInertExp [x1,y1] z1 [x2,y2] z2
  | sameZ && known (> 1) x1 && tcEqType x1 x2 = [ y1 === y2 ]
  | sameZ && known (> 0) y1 && tcEqType y1 y2 = [ x1 === x2 ]
  where sameZ = tcEqType z1 z2
interactInertExp :: [Xi] -> Xi -> [Xi] -> Xi -> [Pair Type]
interactInertExp [x1,y1] z1 [x2,y2] z2
  | sameZ && known (> 1) x1 && tcEqType x1 x2 = [ y1 === y2 ]
  | sameZ && known (> 0) y1 && tcEqType y1 y2 = [ x1 === x2 ]
  where sameZ = tcEqType z1 z2
interactInertExp [x1,y1] z1 [x2,y2] z2
  | sameZ && known (> 1) x1 && tcEqType x1 x2 = [ y1 === y2 ]
  | sameZ && known (> 0) y1 && tcEqType y1 y2 = [ x1 === x2 ]
  where sameZ = tcEqType z1 z2