This puzzle consists completely of binary numbers, so all the characters needed to fill in the squares will be 0s or 1s. The crossword is a 4x4 square grid, so all numbers will be written in binary, with 4 digits; e.g., 1 will be 0001, 2 will be 0010, and 4, 0100. The NOT operation changes all 0s to 1's and all 1s to 0s; e.g., NOT(0110) is 1001 and NOT(1010) is 0101.

Rows (Across): 1. "2 Down" x 2 2. A triangular number * 3. The cube of ("4 Down" - 2) 4. "3 Across" + "3 Down"	Columns (Down): 1. NOT "2 Across" 2. NOT "1 Across" 3. "2 Across" x 2 4. "4 Across" - "1 Across"
* HINT: A triangular number is the number of dots in an equilateral triangle uniformly filled with dots. For example, three dots can be arranged in a triangle; thus three is a triangle number.

1 21 3 4 2 3 4