Description: Define a commuted bra and ket juxtaposition used by Dirac notation. In
Dirac notation, | A >. <. B | is an operator known as the outer
product of A and B , which we represent by ( A ketbra B ) .
Based on Equation 8.1 of Prugovecki p. 376. This definition, combined
with Definition df-bra , allows any legal juxtaposition of bras and
kets to make sense formally and also to obey the associative law when
mapped back to Dirac notation. (Contributed by NM, 15-May-2006)(New usage is discouraged.)