How many stereoisomers does 1,2-di(prop-1-en-1-yl)cyclopropane have? (Count enantiomers, ring diastereomers and E/Z isomers as distinct.)

The ring is symmetric. Cis ring (mirror plane): (E,E) and (Z,Z) are meso (2 isomers), while (E,Z) is chiral, giving an enantiomeric pair (2). Trans ring (C2 axis): (E,E), (Z,Z) and (E,Z) are each chiral and exist as pairs (6). Total $4+6=10$ (checked by enumeration), not $2^4=16$.