unsolved

The flying saucer is yet an unsolved mystery.

And keeping the satellite's huge beam and the distant rectenna reliably synced up also stands as an unsolved technical issue.

Another problem of minimality also remains unsolved—to wit, what is the smallest number of digits a puzzle maker can place in a starting grid and still guarantee a unique solution?

The unsolved mystery baffled investigators for years.

There are many unsolved problems in the field of science.

The case remains unsolved despite extensive investigations.

The unsolved crime haunted the small town for decades.

The unsolved puzzle left everyone scratching their heads.

The unsolved murder case was reopened after new evidence came to light.

The unsolved equation stumped even the most brilliant mathematicians.

The unsolved disappearance of the hiker sparked widespread concern.

The unsolved riddle continued to perplex scholars for generations.

Despite numerous attempts, the code remained unsolved.