caaaar caaadr caaar caadar caaddr caadr caar cadaar cadadr cadar caddar cadddr caddr cadr car cdaaar cdaadr cdaar cdadar cdaddr cdadr cdar cddaar cddadr cddar cdddar cddddr cdddr cddr cdr

car #define car (   x )    (((pair_type *) x)->pair_car) Unsafely access a pair's car