Thanks again Kirky for your patience and putting me on the right track.I have the following pairs:
7a &12a ;14a &23a;24a &25a; 27a &2d;9d &13d ;18d &19d .
I've got 'c' for 20d but can't see an L or R to go with it. Maybe my pairs are'nt quite correct.
Cheers.