Do, show and identity statements

These statements allow analysis and manipulation of atom properties and names.

• SHOW ELEMent (AtomArray) (selection)
  lists elements and defines $result
• SHOW AVERage (AtomArray) (selection)
  SHOW RMS (AtomArray) (selection)
  SHOW SUM (AtomArray) (selection)
  SHOW NORM (AtomArray) (selection)

   
  show element (resid) 
     (name ca and (resid 5 and name ca) around 5.0)
  
   show average (x) (name ca)
  

• DO (expression) (selection)

  do (b = b + x^2 + y^2 + z^2) (all)
  

• IDEN (STOREi) (selection)
  defines a STORE to be used in atom selection later