{\displaystyle \mathbb {R} ^{4}}" is my usual answer to that question, but this recent resolution to a graph problem makes for a great story, too: www.quantamagazine.org/maths-bunkbe...
{\displaystyle \mathbb {R} ^{4}}" is my usual answer to that question, but this recent resolution to a graph problem makes for a great story, too: www.quantamagazine.org/maths-bunkbe...