Passing variables between Apache Velocity and Groovy

{{velocity}}
  #set ($vnumber = 42)
{{/velocity}}

{{groovy}}
  // velocity "$vnumber" is groovy "vnumber"
  gnumber = vnumber
  // following line prevents print out of gnumber
  assert gnumber instanceof Integer
{{/groovy}}

{{velocity}}
  ## groovy "gnumber" is velocity "$gnumber"
  Number: $gnumber
{{/velocity}}