go =>
  S1 = "string",
  println(s1=S1),
  S2 = S1,
  S2[1] := 'x', % also changes S1
  println(s1=S1),
  println(s2=S2),
  nl,

  S3 = "string",
  S4 = copy_term(S3),
  S4[1] := 'x', % no change of S3
  println(s3=S3),
  println(s4=S4),

  nl.