H:   help
M:   matlab line       (execute a matlab line)
D:   Declare a vector      vec :  |vec>
           or an operator   op :  [op]
           or a constant    c1 :  (c1)
     example:
     Dirac  : D: |a> |b> |psi> [L] [Xz] (c1) (c2)
     ....... declares Dirac vectors a,b, psi
                      operators     L  and Xz
                      constants     c1 c2
G:   show the global objects
   example:
     Dirac  : G:
     DECLARED :  |a> |b> |psi> [L] [Xz] (c1) (c2)

$    exit Dirac
     a new call Dirac preserves the global names 
     and their values
General examples:
e:   this command will list the 2-components examples
E:   this command will list the 3-components examples