Reversible design of Two pair Two rail checker:

The two pair two rail checker is required for testing that the outputs in CTSG blocks are complementary or not. Thus the efficient reversible design of two pair two rail checker is discussed in this section. The error checking functions required in the two pair rail checker are as follows
                                                                         E1=x0y1+y0x1
                                                                         E2= x0x1+y0y1
                                                     Where x0/y0 & x1/y1 are complementary,
The two pair rail checker produces the complementary output at E1& E2, if the inputs passed to it are complementary. If the inputs are not complementary, the outputs E1 & E2 will be identical