csquare_rel_def: renamed k to K
Added Krzysztof's theorems subst_elem, not_emptyI, not_emptyE
empty_fun: generalized from -> to Pi
Changed succ(1) to 2 in cmult_2; Simplified proof of InfCard_is_Limit
Added Krzysztof's theorems singleton_eq_iff, fst_type, snd_type
Renamed doubleton_iff to doubleton_eq_iff
Added Krzysztof's theorem disj_imp_disj
Added comments and Id: marker.
Added comments and Id: marker.