3-SAT is an NP-Complete problem. Now given a 3-SAT instance it can be transformed to a Monotone-1-in-3 SAT instance thus even Monotone-1-in-3-SAT is NP-Complete (am aware of this reduction).
But, as I have read (forgot the source) even Cubic-Monotone-1-in-3-SAT is NP-Complete. Assuming given a Monotone-1-in-3-SAT instance how do we reduce it to the 'Cubic-Monotone' version i.e. each boolean variable in the 1-in-3-SAT instance occurs exactly 3 times and only positively.
Can someone please help with this reduction (as simple as possible)?
I tried thinking and searching but couldn't find any simple reduction.