Passage: In March 1970, Larry D. Nichols invented a 2×2×2 "Puzzle with Pieces Rotatable in Groups" and filed a Canadian patent application for it. Nichols's cube was held together by magnets. Nichols was granted U.S. Patent 3,655,201 on 11 April 1972, two years before Rubik invented his Cube.

Question: When did Nichols file for a patent of his cube?
March 1970