Across
1
Lines that never intersect
5
Symbol representing unknown value
6
The number representing nothing
8
Exact correspondence on both sides
9
System of ordered marks for measuring
Down
1
Number divisible only by 1 and itself
2
Number greater than zero
3
Difference between highest and lowest values
4
Closed shape with straight sides
7
Number with digits after a point
9
Collection of distinct elements