Features:

• Exchange of roles by wB/wS duo (Assisting dynamically bK to move to mating square and guarding the mating piece - vs - guarding bK's fields).
• Two out of Four moves are BTB moves.
• The mating as well as guarding of squares by mating piece on mating moves are due to BTB effect.
• bK occupies the square vacated by black piece in both the solutions.
• B1 is to the same square which activates wR for the next BTB move .

(Authors)