if (has_sympy()) {
  ls()
  def_sym(n1, n2, n3)
  ls()
  def_sym("x1", "x2", "x3")
  ls()
  # def_sym("x1", "x2", "x3", warn = TRUE) # Do not run as will cause a warning
  ls()
  def_sym(i, j, charvec = c("x", "y"))
  ls()
}
if (has_sympy()) {
  def_sym(z1, z2, z3)
  u <- paste0("u", seq_len(3))
  ## Creates symbols u1, u2, u3 and binds to names u1, u2, u3 in R.
  def_sym_vec(u) 
  ## Same as (but easier than)
  def_sym(u1, u2, u3)
  ## Notice: this creates matrix [u1, u2, u3]
  as_sym(u)
 }
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