Thanks! It's not obvious for me because I'm forced to use Google Translate.

if you have a slice of bread between two other slices of bread, then it's a bread sandwich. Additionally, if you have a bread sandwich between two other slices of bread, you get a bread sandwich sandwich, and so on.

Because you can only have one bread as the first and the rest are sandwiches as the fillings

assert.equal(slicesToName(11),'bread sandwich sandwich sandwich sandwich sandwich') - why not 'bread sandwich bread sandwich bread sandwich sandwich'?