D x (y1. x (y2. x (y3. x (y4. y1 y2 y3 y4))))\r
C x (y1. x (y2. x (y3. x (y4. y1 y2 y3 y1))))\r
C x (y1. x (y2. x (y3. x (y4. y1 y2 y1 y4))))\r
D x (y1. x (y2. x (y3. x (y4. y1 y2 y3 y4))))\r
C x (y1. x (y2. x (y3. x (y4. y1 y2 y3 y1))))\r
C x (y1. x (y2. x (y3. x (y4. y1 y2 y1 y4))))\r