In Landulph's chamber, what steps are safe?

Hint 1 of 5:

Did you study the rune tapestry in the Raven Room?

Hint 2 of 5:

If so, you may have noticed that R is the rune for travel.

Hint 3 of 5:

When going up, select only the steps containing the R rune.

Hint 4 of 5:

When coming down, you cannot see the runes.  I hope you wrote down what steps
you took on the way up!