{def S1 hello world}    // set S1 to "hello world"
-> S1
{S1}                    // get the value of S1
-> hello world

{def S2 S1}             // define S2 as S1
-> S2
{S2}                    // the value of S2 is S1
-> S1
{{S2}}                  // get the value of the value of S2
-> hello world

{def S3 {S1}}           // set S3 to the value of S1
-> S3
{S3}                    // get the value of S3
-> hello world