You are confusing yourself when trying to reduce it from the actual expression to single letter variables. On referring the actual link, it would appear that the variables you use can be mapped to the original expressions as follows:
A = speed > 2000
B = memory > 512
C = speed <= 2000
D = memory <= 512
If you look at it, C
equals !A
and D
equals !B
. So the expression (C || D)
is effectively !((!A) || (!B))
. By De Morgan's Law, that is the same as !(A && B)
.