Copyright (c) 2003 Jorge Nuno Silva
This game is played on the following board:
Usually, a player will prefer to swap enemy isolated pieces, because he will increase the move range of his upper stones.
White threats a win by swapping c4 (which will be protected one turn by the Ko rule) and then d3-c4 (making a diagonal 3 in-a-row).
However, Black replies with c1-c2 (can win next turn with e3-d2). So White replies d2, then c2-c3 (e3-d4 threat), d4, c3-c4 and the White first threat ended.