Highlight duplicates from four or more separate range in the same sheet

I want to highlight duplicate value in four separate range for a lessons schedule using conditional formatting in google sheets, in this example there are four classes,

what i'm trying to achieve are :

1. in lesson 1 class A, B, C & D all have different subject so they won't be highlighted
2. in lesson 2 class A and class D have the same subject, so the same subject "Ipa" will be higlighted in both class A and class D
3. in lesson 3 class A, B and C have the same subject so the same subject "Bing" will be highlighted in class A, B and C

is anyone know the formula for this? or is it possible the achieve this if they're four separate cells rather than four separate range?