#print
So far all the special characters in the substitute
command are used to select the string to be replaced.
There is one character used in the new string to be inserted.
It is '&' which when used on the right hand side of a substitution,
refers to the expression given on the left hand side.
For example, the command

s/the/&m/

changes "the" into "them".  Try that on file "text";
then rewrite the file and type "ready".
#create Ref
we went to see them yesterday.
#create text
we went to see the yesterday.
#user
#cmp text Ref
#log
#next
36.2b 5