Twin - two or more problems which are slight variations on each other, composed by the same person. The variation is usually brought about by adding, removing or moving a piece in the initial setup. (http://en.wikipedia.org/wiki/Chess_problem_terminology#T)
Twin problems — two (or more) separate but closely related positions — offer tantalizing challenges to composer and solver alike. Sometimes the two positions are identical except that one is shifted up, down, left, or right; often a single piece is relocated. The solutions, of course, though often thematically related, are always different. (Outrageous Chess Problems by Burt Hochberg, 2005, 128 pages)
The following twins were composed by Joselito Marcos from the Philippines. Marcos, a resident of Papua New Guinea since early 1996, is a member of PNG chess federation and has represented PNG in the 2009 Oceania zonal chess championship held in Gold Coast, Australia. He is a member of the PNG team to the 35th chess Olympiad held in Bled, Slovenia in 2002. He has won undefeated the last PNG chess championship in 2003.
White mates in 4
(B) Move the black pawn at d7 to b7
Drag your mouse to view the solutions from here Solution (A): 1.Ba7! h4 2.Rb1 h3 3.Rb6! (forming a battery) Kd4 4.Rb4#; Solution (B): 1.Bb6! h4 2.Re1 h3 3.Re6! (a battery is formed only after Black's next move)Nxb6 4.Re4# to here.