Plus fast!

I noticed an ad in the métro claiming that some… product (I don’t recall what it was) was in fact “faster!” (than other competing products, I assume). What interested me was the fact that the phrase in French, “plus vite” (literally more fast), could be iconically abbreviated by swapping in the + sign for the word “plus”. Commenting on this fact sparked a long discussion about the words for mathematical operations in French and English. We think of ‘addition’ as a symmetrical function, but adding (as in, say, milk to cereal) does not appear to be symmetrical. Is this a semantic or pragmatic feature of ‘add’? Those who know me will not be surprised that I typically would vote for pragmatic, but it’s rather difficult to see how to work that out in this case. More as I think about it.