Yeah, I think the story is that Penrose saw an illusion in an Escher print that encouraged him to create the Penrose Triangle, his dad Lionel created the Penrose staircase, and then sent a copy of these in the paper "Impossible objects..." to Escher, who then used the staircase in "Ascending and Descending" and others. It's kind of cool that they cite eachother in these works as inspiration here. I bet Escher could have made an interesting print of them pointing at one another in some kind of impossible object.

And apparently neither Penrose nor Escher knew about Oscar Reutersvärd's work! Oscar got robbed lol.

In 1954, Escher inspired Roger Penrose to create the impossible triangle. Roger shared this with his father, Lionel, who then designed the impossible staircase. In 1958, they published a paper on these illusions and sent a copy to Escher. Escher used Lionel's staircase to create Ascending and Descending and Roger's triangle to create Waterfall. Both Penrose and Escher were completely unaware that Oscar Reutersvärd had independently invented these shapes earlier.