Arithmetic expressions grammar transformation
The missing step:

E --&gt; P T
T --&gt; B E T |


rewrite E in T:

E --&gt; P T
T --&gt; B P T T | 


Simplify T:

E --&gt; P T
T --&gt; B P T | 


Equivalent to:

E --&gt; P T
T --&gt; {B P}


And there you are.