old_contents: """
  Line Chart with Sequence Generator
  ----------------------------------
  This examples shows how to create multiple lines using the sequence generator.
  """
  # category: line charts
  
  import altair as alt
  
  source = alt.sequence(start=0, stop=12.7, step=0.1, as_='x')
  
  alt.Chart(source).mark_line().transform_calculate(
      sin='sin(datum.x)'
  ).transform_calculate(
      cos='cos(datum.x)'
  ).transform_fold(
      ['sin', 'cos']
  ).encode(
      x='x:Q', 
      y='value:Q', 
      color='key:N'
  )
  
new_contents: """
  Line Chart with Sequence Generator
  ----------------------------------
  This examples shows how to create multiple lines using the sequence generator.
  """
  # category: line charts
  
  import altair as alt
  
  source = alt.sequence(start=0, stop=12.7, step=0.1, as_='x')
  
  alt.Chart(source).mark_line().transform_calculate(
      sin='sin(datum.x)',
      cos='cos(datum.x)'
  ).transform_fold(
      ['sin', 'cos']
  ).encode(
      x='x:Q', 
      y='value:Q', 
      color='key:N'
  )
  
subject: Modify generator example to use single calculation transform