selectLB

  
Purpose 		

Select Lie brackets of certain order in a given expression.





Syntax 		 
e:=selectLB(x,k,s)




Description 		 

Selects the Lie brackets in a given expression x which are of
order smaller, equal or greater than k, according to whether
the third argument s is less, equal or greater than zero,
respectively.





Arguments 		
$x$  Expression containing Lie brackets (list, sum,
etc.).


 		 $k$ Bracket degree (also referred to as order or length).


 		 $s$ $\parbox{0.64\textwidth}{
 $< 0$\ - Select brackets of order $< k$.\\...
...- Select brackets of order $= k$.\\ 
 $> 0$\ - Select brackets of order $> k$.}$




Examples 		

Consider the expression zr in the example for the function
reduceLB on page .  The the summation of 
brackets of order $2$ can be obtained by invoking:
> selectLB(zr,2,0);

  (1/2 u0_1~ u2_2~ - 1/2 u2_1~ u0_2~) (f0~ &* f2~)

     + (- 1/2 u1_1~ u0_2~ + 1/2 u0_1~ u1_2~) (f0~ &* f1~)

     + (- 1/2 u2_1~ u1_2~ + 1/2 u1_1~ u2_2~) (f1~ &* f2~)