# this demos some of the logical operators.  Note the operations return "1.0" 
# to indicate true, "0.0" to indicate false.  For input, all tests should
# use 0 to mean false, non-zero to mean true.
d= findgen(2000)
l1= d .gt( 100 )
l2= d .lt( 1900 )
l3= l1 .and( l2 )
l4= l1 .or( l2 )
l5= not( l3 ) # this demoes a problem where this isn't going to Ops.not.