I could cross-check you could cross-check he could cross-check we could cross-check you could cross-check they could cross-check
V-ing form
I could be cross-checking you could be cross-checking he could be cross-checking we could be cross-checking you could be cross-checking they could be cross-checking
Perfect
I could have cross-checked you could have cross-checked he could have cross-checked we could have cross-checked you could have cross-checked they could have cross-checked
V-ing perfect
I could have been cross-checking you could have been cross-checking he could have been cross-checking we could have been cross-checking you could have been cross-checking they could have been cross-checking
Negation
Simple form
I could not cross-check you could not cross-check he could not cross-check we could not cross-check you could not cross-check they could not cross-check
V-ing form
I could not be cross-checking you could not be cross-checking he could not be cross-checking we could not be cross-checking you could not be cross-checking they could not be cross-checking
Perfect
I could not have cross-checked you could not have cross-checked he could not have cross-checked we could not have cross-checked you could not have cross-checked they could not have cross-checked
V-ing perfect
I could not have been cross-checking you could not have been cross-checking he could not have been cross-checking we could not have been cross-checking you could not have been cross-checking they could not have been cross-checking
Interrogative form
Simple form
could I cross-check? could you cross-check? could he cross-check? could we cross-check? could you cross-check? could they cross-check?
V-ing form
could I be cross-checking? could you be cross-checking? could he be cross-checking? could we be cross-checking? could you be cross-checking? could they be cross-checking?
Perfect
could I have cross-checked? could you have cross-checked? could he have cross-checked? could we have cross-checked? could you have cross-checked? could they have cross-checked?
V-ing perfect
could I have been cross-checking? could you have been cross-checking? could he have been cross-checking? could we have been cross-checking? could you have been cross-checking? could they have been cross-checking?
Interro-negative form
Simple form
could I not cross-check? could you not cross-check? could he not cross-check? could we not cross-check? could you not cross-check? could they not cross-check?
V-ing form
could I not be cross-checking? could you not be cross-checking? could he not be cross-checking? could we not be cross-checking? could you not be cross-checking? could they not be cross-checking?
Perfect
could I not have cross-checked? could you not have cross-checked? could he not have cross-checked? could we not have cross-checked? could you not have cross-checked? could they not have cross-checked?
V-ing perfect
could I not have been cross-checking? could you not have been cross-checking? could he not have been cross-checking? could we not have been cross-checking? could you not have been cross-checking? could they not have been cross-checking?