WHAT GOES UP MUST COME DOWN

Lewis Rothlein is a yoga instructor and onetime journalist in Asheville, N.C. He teaches a popular course on "The Art of Solving Crosswords" for senior citizens at the University of North Carolina in Asheville. Jeff Chen is a writer in Seattle. They exchanged over 100 emails, back and forth, just brainstorming this puzzle's theme.

Lewis has had five previous puzzles in The Times, all Thursdays. Jeff is a regular contributor here.

LEWIS: I love working with Jeff because he's a good listener, leaves no stone unturned in his quest for a polished grid, and is crackerjack smart. And while we agree on the most important puzzle-making priorities, we often come at things from different angles, which makes for a lively and productive back-and-forth.

Take our brainstorming. The following took place over several weeks. We were discussing a theme involving AND/OR, and one of us said, "How about giving this theme a game show angle?", which led to a quiz-show-sounding "Name two terms related to…", from which the word "name" triggered the phrase "name drop," which suggested taking horizontal words that have names embedded and having the names drop down from them in the grid, which led to "Nah, turning-type puzzles are too common," which sparked, "Not if we can come up with a new variation," which brought us to today's theme.

Neither of us could recall seeing a puzzle where the solver had to go one way, then the other, through a string of letters. When we found phrases that allowed this to happen, we thought they were cool and thought many solvers would think so as well.

Hopefully, the journey from AND/OR to "What goes up, must come down" was fruitful, and you enjoyed this!

JEFF: Lewis comes up with interesting concepts. He's a fun guy to bat ideas around with, and he's incredibly receptive to tangential exploration. We've worked on a few projects together now, and we've never ended exactly where we started — sometimes doing something completely different.

It's such a pleasure to work with him. Mainly just ups!

I enjoy having a crunchy problem to wrap my brain around. This one wasn't as hard as others — it's a simple matter to search for palindromic letter patterns buried within phrases — but it was still a fun diversion. I doubted we were going to find anything of interest, and I didn't think the strings would be long enough to be worthwhile discoveries, but I was pleasantly surprised.

As usual, shows what I know!

We even had the option of using only long(ish) strings that happened to be words in their own right (like PLAN and OMEN). We debated the merits of that approach, but eventually decided to pick the longest strings that were buried within the most colorful base phrases.

The grid was a bear, as crossing pairs of theme entries are notoriously difficult to grid around. Some of the palindromic strings weren't friendly, either. I struggled getting the skeleton together — all those crossing themers taking up so much real estate — until finally landing on a fortuitous overlap, COURSE CREDIT enabling a workable grid backbone.

I usually advise sticking to 140 words to achieve a strong balance of color and cleanliness, but taking out a black square at the first S of CLASS SIZE bizarrely seemed to help. It made sense after studying the area — four letters ending in O gives more choices than three letters ending in O — but I wasn't wild about ENIAC. We kept banging away at that section, and couldn't come up with anything better at 140 words, so it was what it was. Ah well, hopefully nerds everywhere are okay with it. Beep boop.