Place a given number of black and white circles in every row, column and thickly outlined region. Wherever two black and two white circles form a 2x2 checkerboard pattern, a Battenburg marking is given. Some circles are already placed.
(Rules (modified) and example (3 blacks and whites each) from WPC 2017 IB)
History of the puzzle
Battenburg Sudoku first appeared on Bram de Laat's (Netherlands) website in 2013 as a part of Daily League Sudoku series. This puzzle was developed as a practice material for the said puzzle. 
The name comes from Battenburg markings used for emergency services in the UK and other regions. 
Appearances in the past WPCs
- WPC 2017/Round 13 by Prasanna Seshadri