I have 25 statements
If $A$ , then $B$ .
If not $C$ , then not $B$ .
If $C$ , then $D$ .
If not $E$ , then not $D$ .
If $E$ , then $F$ .
If not $G$ , then not $F$ .
...
If $W$ , then $X$ .
If not $Y$ , then not $X$ .
If $Y$ , then $Z$ .
What can we conclude from all statements above?
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The contrapositive of any logically true statement is always true.
Hence, "If not $C$ , then not $B$ " is equivalent to "If $B$ , then $C$ ;" "If not $E$ , then not $D$ " is equivalent to "If $D$ , then $E$ ;" and so on.
Thus, we have a series of statements that, following a sort of transitive property for logically true statements, reduce to "If $A$ , then $Z$ ," whose contrapositive is "If not $Z$ , then not $A$ ."
"If $Z$ , then $A$ " cannot be concluded because the converse of a logically true statement is not necessarily true.
Regarding the other 2 options, we cannot conclude anything about $A$ and $Z$ , individually, because the essence of "if, then" statements is that the truth of the conclusion is dependent on truth of the premise.