What is the opposite of this condition? Condition: $(A=1) \land (C>1) \land (B<6)$
Opposite Condition: $(A\ne 1) \lor (C\le 1) \lor (B\ge 6)$
Is that true?  

You are right:
\begin{align*}
&&\lnot((A=1) \land (C>1) \land (B<6))\\
&\Longleftrightarrow&\lnot(A=1) \lor \lnot(C>1) \lor \lnot(B<6) \\
&\Longleftrightarrow&(A \ne 1) \lor (C\le 1) \lor (B \ge 6)
\end{align*}
