Reference: OPINTERVAL
[a, b] returns the set of all integers between a and b, inclusively. [a, b, δ] returns the set of all real numbers a, a + δ, a + 2δ, ... less than or equal to b.
[a, b] returns the set of all integers between a and b, inclusively. [a, b, δ] returns the set of all real numbers a, a + δ, a + 2δ, ... less than or equal to b.