Complex sentence: Letterisms founder, Jean-Isidore Isou notice, noted that Dadaism had chiseled art down to the word, what Letterism had intended to do was refine it to the letter, hence its name.
Split into simpler sentences: Letterisms founder, Jean-Isidore Isou notice, noted that Dadaism had chiseled art down to the word. What Letterism had intended to do was refine it to the letter, hence its name.