disteromer covers very wide range. infact...............mirror image-(enantiomers+identical) = disteromer.

the condition 4 disteromer is that mirror image is superimposable. and the molecule lack symmetry.  generally geometrical isomers are symmetrical ther4 geometrical isomers can b treated as distremer. if G.I due 2 double bond then clearly image is superimposable. if no double bond then symmetry can be judged by R,S config.