prop(Obj,user_action,skips) <- prop(Obj,length,long). prop(Obj,user_action,reads) <- prop(Obj,length,short) & prop(Obj,thread,new). prop(Obj,user_action,reads) <- prop(Obj,length,short) & prop(Obj,thread,follow_up) & prop(Obj,author,known). prop(Obj,user_action,skips) <- prop(Obj,length,short) & prop(Obj,thread,follow_up) & prop(Obj,author,unknown).