"Eric" wrote...
There is a list of value in column A
1,5,6,8,9,10,3,20
There is a given value in cell B1, which is 4
The value of range is 1 in cell D1
I would like to determine whether the value 4 in cell B1 +/- 1 in cell D1
[value of range] is matching any value in column A.
In this case, the matching values are between 3 [4-1] and 5 [4+1], and 5
exists in column A, then the value 4 in cell B1 is valid, and return true
in cell C1.
....

And, FTHOI, using ABS and avoiding volatile functions.

=SUMPRODUCT(--(ABS(A1:A8-B1)<=D1))