\input arrows.tex $$ \vcenter{ \def \hfq{\hfil \ } \offinterlineskip \halign{ % preamble &\hfq #\hfq \cr $t$& \vrule depth 5pt & $-1$&& $0$&& $1$&& $2$& \cr \noalign{\hrule} $x' (t)$& \vrule height 10pt depth 3pt & $-2$& $-$& $0$& $+$& $2$& $+$& $4$& \cr \noalign{\hrule} \bbuucenter{$x (t)$}& \vrule& \bbup{$2$}& \brightdownarrow & \down{$1\strut $}& \brightuparrow & \bup{$2$}& \bup{\brightuparrow} & \bup{\bup{$5$}} \cr \noalign{\hrule} $y' (t)$& \vrule height 10pt depth 3pt & $-4$& $-$& $-2$& $-$& $0$& $+$& $2$& \cr \noalign{\hrule} \bbuucenter{$x (t)$}& \vrule& \bbuup{$5$}& \bbup{\brightdownarrow} & \bup{$2$}& \brightdownarrow & \down{$1$}& \bbrightuparrow & \bbup{$2$} \cr }} $$ \bye