You have missed it.
Y have no immediate predecessor in Standard Math framework, exactly because d value is a non-finite regression, such that this non-finite regression > 0.
If the term all is used, then there is no non-finite regression > 0, and d=0 (there is no other way, because if we use all on the non-finite, then d (which is an absolute value) must have the minimal absolute value, which is 0) .
In that case X<Y=X+0, is false.
Standard Math is based on a contradiction, in this case, because it claims that:
d > 0 (there is no immediate predecessor to Y) AND d=0 (the non-finite universe between X and Y, is completely filled).
EDIT:
"there is always another real number between any two real numbers" = "a non-finite regression of d value" = "the non-finite universe between X and Y is not completely filled"