\(\overrightarrow{R} \overleftarrow{R} \leftarrow \rightarrow\)
and with overset\(\overset{\rightarrow}{R} \overset{\leftarrow}{R} \leftarrow \rightarrow\)
and with long versions of the commands\(\overset{\longrightarrow}{R} \overset{\longleftarrow}{R} \leftarrow \rightarrow\)
and with underset for arrows below the letter\(\underset{\rightarrow}{R} \underset{\leftarrow}{R} \leftarrow \rightarrow\)