Does a 3SAT instance need to have exactly three terms in each clause?

Question

For example, is

(x \/ ~y ) /\ (~x \/ y \/ ~z)

valid?

I have read conflicting descriptions of 3SAT where some say you must have exactly 3 terms in each clause, others say at most 3.

if you have 2 terms (no corresponding z), like in the first clause, how can one handle this ? Can you just pad this out to be (x \/ ~y \/ False )?

Answer 1

To convert a clause with 2 variables into 3 you can do this - $(a \lor !b) \equiv (a \lor !b \lor c) \land (a \lor !b \lor !c)$. The clause is equivalent since the values of $a$ and $b$ are independent of the value of $c$.