Can You Program with $\LaTeX$?

1. $\TeX$ primitive:
   
   \def{\Greetings}{\textbf {Greetings from Vikin-GO}}
   
2. $\LaTeX$ command:
   
   \newcommand{\Vector}[1]%Number of arguments
{
       \underline { \textbf {#1} }
}
\newcommand{\Matrix}[1]%Number of arguments
{
       \underline {\underline { \textbf {#1} } }
}