/ c c\ (c - d)*|----- + -| \c - d d/ ------------------- c
(c - d)*(c/(c - d) + c/d)/c
c*d + c*(c - d) --------------- c*d
c c d -1 + - + ----- - ----- d c - d c - d
-1 + c/d + c/(c - d) - d/(c - d)
/1 1 \ (c - d)*|- + -----| \d c - d/
(c - d)*(1/d + 1/(c - d))