This is an example solution I am reading but I can't understand the 3rd transformation.
I understand changing the LHS to
< ---a (this)
using set diff representation
(The notes I am reading use this notation where sometimes the intersection operator is "big", does it have an alternate meaning when it is big, or simply a typo?)
If it is just a typo, then I needn't worry about it.
but the next step I don't understand:
(to this) b --->
the notes claim this is using distributivity,
but I can't see how they arrive at that equation using this rule
<-- this I understand,
but I can;t see how they went from a to b