I have the following code, which needs 2 sub-columns in the last main column. I have written code as follows:

\begin{table}
  \centering
    \begin{tabular}{|c|l|c|c|}
    \hline
    \multicolumn{1}{|c|}{\bfseries First} &amp; \multicolumn{1}{|c|}{\bfseries Characteristics} &amp; \multicolumn{2}{|c|}{\bfseries Implemented in}\\ A&amp;B \\ \hline
    a &amp; b &amp; c &amp; d \\
    1 &amp; 2 &amp; 3 &amp; 4\\
    \end{tabular}
\end{table}


The result is



I want the "A" and "B" as sub-column within the "Implemented in" column.


Question: Why is the result not 1?
Answer: ANSWER: An assignment evaluates side effects before performing the assignment.

m += m++;


is equivalent to

temp = m + m++;    ; m is now 1, but temp is 0
m = temp;          ; m is now 0 again