Owning chometz: what to do if you accidentally find chometz in your house on Pesach?

Topics: Tosafos: rectifying negative commandment with positive commandment; “is it okay to steal if you intend to return the item at a future date? vs “is it okay to own chometz if you intend to destroy it at a later date?”; active transgression vs passive transgression; receiving a gift of chometz on Pesach by accident;