Standard constructors:

[a,b] ( a b -- interval )

(a,b) ( a b -- interval )

[a,b) ( a b -- interval )

(a,b] ( a b -- interval )

One-point interval constructor:

[a,a] ( a -- interval )

Open-ended interval constructors:

[-inf,b] ( b -- interval )

[-inf,b) ( b -- interval )

[a,inf] ( a -- interval )

(a,inf] ( a -- interval )

The set of all real numbers with infinities:

[-inf,inf] ( -- interval )

The empty set:

empty-interval

Another constructor:

points>interval ( seq -- interval nan? )