What is the meaning of this sentence?

Question

Please see the below sentence:

Namely, $A$ and $B$ are equivalent iff setting any variable $x$ to $false$ resp. $true$ yields two respectively equivalent DNF/CNF pairs.

What is the meaning of "$false$ resp. $true$"?

Answer 1

The entire sentence says, in clearer words:

$A$ and $B$ are equivalent iff setting any variable $x$ as false in $A$ and true in $B$ yields two equivalent DNF/CNF pairs.

Intuitively, the truth tables of $A$ and $B$ have identical outputs.

The abbreviation means "respectively", and is a rather common word used in logic texts to associate two different things to two different other things unambiguously. "A and B... C resp. D" associates A with C and B with D.