interval<= ( i1 i2 -- ? )
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Vocabulary
math.intervals

Inputs

i1	an interval
i2	an interval

Outputs

?	a boolean or incomparable

Word description
Compares i1 with i2, and outputs one of the following:

•	t if every point in i1 is less than or equal to every point in i2
•	f if every point in i1 is greater than every point in i2
•	incomparable if neither of the above conditions hold

Definition

USING: combinators kernel ;

IN: math.intervals

: interval<= ( i1 i2 -- ? )
    {
        {
            [ 2dup [ special-interval? ] either? ]
            [ incomparable ]
        }
        {
            [ 2dup interval-intersect empty-interval? ]
            [ (interval<) ]
        }
        { [ 2dup right-endpoint-<= ] [ t ] }
        [ incomparable ]
    } cond 2nip ;