Let L = 16, M = 15, NL = 19, n = L-M, the value of the expression n & n-1? What does n & n mean?

Let L = 16, M = 15, NL = 19, n = L-M, the value of the expression n & n-1? What does n & n mean?

L = 16 & L numerical type
M = 15 & M numerical type
NL = 19 & & NL numerical type
N = "L-M" & n character type
*Mistake: think about [& n] first and then [n & n], that's wrong
*Correct: [& n] has no priority
*First [letter N] and then macro replacement [& n = "L-M"]
*Namely: nl-m
N & n-1 & equivalent to
Nl-m & & 19-15 result should be 4
Although not verified, but the idea is correct
It's too late to answer,
If you understand and the results are right,
One's own experience is not plagiarized. If it's the same, it's a coincidence
Supplement:
Just now, I lost 1. Let the downstairs savage copy and modify it. Wipe it
N&N=4,N&N-1=3