"The main functionality of this is in the texting space," he says. Typing the symbol he has devised with a single keystroke will save time and – crucially, in the context of Twitter – two characters. It may seem a strange digression for a man whose cafe-cum-restaurant empire encompasses 10 businesses, but he's serious enough about it that he has invested plenty of time and about $75,000 of his own money in it so far. He has developed the typography – effectively an upper-case "T" and a lower-case "h" bunched together so they share the upright stem – and an app that puts it in everyone's hand by allowing users to download an entirely new electronic keyboard complete not just with his symbol – which he pronounces "th" – but also a row of keys containing the 10 or 15 (depending on the version) most frequently typed words in English.* "Is this important?" he asks rhetorically. "No. Is this going to change the world? Not really. But is it something that might be useful for people? I think so." So far, though, the take-up has been minimal. But that might change if he can get his innovation into Apple's app store. The problem is, the Californian tech giant has so far resisted his advances.

"Apps should be engaging and exciting, enabling users to do something they couldn't do before; or to do something in a way they couldn't do before or better than they could do it before," the company wrote to Mathis in rejecting his app. They did, however, invite him to add features that would help his app "deliver a robust user experience". Mathis insists he doesn't see his app as a money-making venture. "Though I would like to recover the costs, if possible," he adds. But one of the issues he faces in getting past the Apple gatekeepers is that his app is essentially a modification of the keyboard component of the operating system – and that is a big no-no in the Apple universe. It's not only Apple that is sceptical, though. Mathis has copped criticism on Twitter (one correspondent called him "a crazy arsehole") from people who claim he is attempting to trademark a symbol that has long been in use as part of the Serbian Cyrillic alphabet (pronounced "tshe", the letter represents the "ch" sound found in the word "chew"). Mathis concedes the likeness, but insists he was a long way down the road on his project before he became aware of it. Over lunch in his city eatery Henry and the Fox, he shows me the preliminary sketchwork for "th" on his iPad, and there are lots and lots of iterations. Does it prove the chronology? Perhaps not, but for what it's worth I believe him.

At any rate, time will tell if this is one of Paul Mathis' better ideas or not. Though he realises he might not be around for the vindication – if it comes. "The Benedictine monks developed the modern version of the ampersand in the Middle Ages, when they were hand-copying religious texts," he says. "I'm not putting myself in the same league, but who knows – maybe in 500 years' time people will be amazed that there was a time when we didn't use 'th'." * According to Wikipedia, the 15 most commonly used words in English are, in descending order: the, be, to, of, and, a, in, that, have, I, it, for, not, on, with. twitter: @karlkwin